Bazel CI flaky test failure com.google.devtools.build.lib.buildtool.OutputArtifactConflictTest

CI: https://buildkite.com/organizations/bazel/analytics/suites/bazel-bazel/tests/018e5735-67c6-7cc2-bab1-7e7bce69b076?branch=master

Platform: Centos

Steps:
```
BAZELCI_TASK=centos7
TEST_TARGET=//src/test/java/com/google/devtools/build/lib/buildtool:OutputArtifactConflictTest
TEST_NAME=testConflictErrorAndUnfinishedAspectAnalysis_mergedAnalysisExecution[skymeld=true,minimizeMemory=true,keepGoing=false]
bazel test //src/test/java/com/google/devtools/build/lib/buildtool:OutputArtifactConflictTest --test_filter=testConflictErrorAndUnfinishedAspectAnalysis_mergedAnalysisExecution[skymeld=true,minimizeMemory=true,keepGoing=false]
```

Logs:
```
FAIL: //src/test/java/com/google/devtools/build/lib/buildtool:OutputArtifactConflictTest.
expected to contain any of: [//x:y, //x/y:y, //x:fail_analysis]
but was : []
at com.google.devtools.build.lib.buildtool.OutputArtifactConflictTest.testConflictErrorAndUnfinishedAspectAnalysis_mergedAnalysisExecution(OutputArtifactConflictTest.java:559)
```

CC Greenteam @meteorcloudy