API 21 Emulator is flaky

[api_21_flake.txt](https://github.com/bumptech/glide/files/1485955/api_21_flake.txt)

First set of tests fails with:
```
com.bumptech.glide.load.resource.bitmap.DownsamplerEmulatorTest > calculateScaling_withFitCenter[test(AVD) - 5.0.2] FAILED
Test failed to run to completion. Reason: 'Test run failed to complete. Expected 83 tests, received 80'. Check device logcat for details
Tests on test(AVD) - 5.0.2 failed: Test run failed to complete. Expected 83 tests, received 80
:instrumentation:connectedDebugAndroidTest FAILED
FAILURE: Build failed with an exception.
```

Then the retries fail with:
```
/home/travis/build/sjudd/glide/instrumentation/build/outputs/apk/debug/instrumentation-debug.apk
com.android.ddmlib.InstallException: Unknown failure (Error: Could not access the Package Manager. Is the system running?)
at com.android.ddmlib.Device.installRemotePackage(Device.java:1004)
at com.android.ddmlib.Device.installPackage(Device.java:911)
at com.android.builder.testing.ConnectedDevice.installPackage(ConnectedDevice.java:122)
at com.android.builder.internal.testing.SimpleTestCallable.call(SimpleTestCallable.java:126)
at com.android.builder.internal.testing.SimpleTestCallable.call(SimpleTestCallable.java:52)
at java.util.concurrent.ForkJoinTask$AdaptedCallable.exec(ForkJoinTask.java:1424)
at java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:289)
at java.util.concurrent.ForkJoinTask.externalAwaitDone(ForkJoinTask.java:326)
at java.util.concurrent.ForkJoinTask.doJoin(ForkJoinTask.java:391)
at java.util.concurrent.ForkJoinTask.join(ForkJoinTask.java:719)
at com.android.ide.common.internal.WaitableExecutor.waitForAllTasks(WaitableExecutor.java:215)
at com.android.builder.testing.BaseTestRunner.runTests(BaseTestRunner.java:190)
at com.android.build.gradle.internal.tasks.DeviceProviderInstrumentTestTask.runTests(DeviceProviderInstrumentTestTask.java:151)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.gradle.internal.reflect.JavaMethod.invoke(JavaMethod.java:73)
at org.gradle.api.internal.project.taskfactory.DefaultTaskClassInfoStore$StandardTaskAction.doExecute(DefaultTaskClassInfoStore.java:142)
at org.gradle.api.internal.project.taskfactory.DefaultTaskClassInfoStore$StandardTaskAction.execute(DefaultTaskClassInfoStore.java:135)
at org.gradle.api.internal.project.taskfactory.DefaultTaskClassInfoStore$StandardTaskAction.execute(DefaultTaskClassInfoStore.java:122)
at org.gradle.api.internal.AbstractTask$TaskActionWrapper.execute(AbstractTask.java:762)
at org.gradle.api.internal.AbstractTask$TaskActionWrapper.execute(AbstractTask.java:729)
at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter$1.run(ExecuteActionsTaskExecuter.java:121)
at org.gradle.internal.progress.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:336)
at org.gradle.internal.progress.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:328)
at org.gradle.internal.progress.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:199)
at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:110)
at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeAction(ExecuteActionsTaskExecuter.java:110)
at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:92)
at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:70)
at org.gradle.api.internal.tasks.execution.SkipUpToDateTaskExecuter.execute(SkipUpToDateTaskExecuter.java:62)
at org.gradle.api.internal.tasks.execution.ResolveTaskOutputCachingStateExecuter.execute(ResolveTaskOutputCachingStateExecuter.java:54)
at org.gradle.api.internal.tasks.execution.ValidatingTaskExecuter.execute(ValidatingTaskExecuter.java:58)
at org.gradle.api.internal.tasks.execution.SkipEmptySourceFilesTaskExecuter.execute(SkipEmptySourceFilesTaskExecuter.java:97)
at org.gradle.api.internal.tasks.execution.CleanupStaleOutputsExecuter.execute(CleanupStaleOutputsExecuter.java:87)
at org.gradle.api.internal.tasks.execution.ResolveTaskArtifactStateTaskExecuter.execute(ResolveTaskArtifactStateTaskExecuter.java:52)
at org.gradle.api.internal.tasks.execution.SkipTaskWithNoActionsExecuter.execute(SkipTaskWithNoActionsExecuter.java:52)
at org.gradle.api.internal.tasks.execution.SkipOnlyIfTaskExecuter.execute(SkipOnlyIfTaskExecuter.java:54)
at org.gradle.api.internal.tasks.execution.ExecuteAtMostOnceTaskExecuter.execute(ExecuteAtMostOnceTaskExecuter.java:43)
at org.gradle.api.internal.tasks.execution.CatchExceptionTaskExecuter.execute(CatchExceptionTaskExecuter.java:34)
at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter$EventFiringTaskWorker$1.run(DefaultTaskGraphExecuter.java:248)
at org.gradle.internal.progress.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:336)
at org.gradle.internal.progress.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:328)
at org.gradle.internal.progress.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:199)
at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:110)
at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter$EventFiringTaskWorker.execute(DefaultTaskGraphExecuter.java:241)
at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter$EventFiringTaskWorker.execute(DefaultTaskGraphExecuter.java:230)
at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$TaskExecutorWorker.processTask(DefaultTaskPlanExecutor.java:123)
at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$TaskExecutorWorker.access$200(DefaultTaskPlanExecutor.java:79)
at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$TaskExecutorWorker$1.execute(DefaultTaskPlanExecutor.java:104)
at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$TaskExecutorWorker$1.execute(DefaultTaskPlanExecutor.java:98)
at org.gradle.execution.taskgraph.DefaultTaskExecutionPlan.execute(DefaultTaskExecutionPlan.java:625)
at org.gradle.execution.taskgraph.DefaultTaskExecutionPlan.executeWithTask(DefaultTaskExecutionPlan.java:580)
at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor$TaskExecutorWorker.run(DefaultTaskPlanExecutor.java:98)
at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:63)
at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:46)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:55)
at java.lang.Thread.run(Thread.java:748)
```