Improve library resolution error reporting and handling

I just hit the issue described in #2699, where the server runtime classpath container couldn't be resolved. It was difficult to figure out as there were no real indications of a problem, largely because our logging isn't actually visible (#3092). I ended up having to launch a debug instance and put exception breakpoints on `CoreException` to figure out what was going wrong.

I hit this problem as my Windows VM's networking was non-functional and so attempting to resolve the server runtime artifacts failed (`servlet-api 3.1.0` and `jsp 2.3`). Maven helpfully wrote out its `.lastUpdated` files which prevent subsequent attempts to re-resolve the artifacts because of [m2e's default update policy](https://github.com/GoogleCloudPlatform/google-cloud-eclipse/issues/830#issuecomment-306843936) is set to never update.

Our reliance on Maven to resolve artifacts means that we're subject to m2e's policy decisions. But unlike m2e, we do not have a `pom.xml` to which to attach resolution problems.

We can actually ignore m2e's policies — and we actually do in our `DependencyResolver` (#2887). But it turns out that we have two codepaths for resolving maven artifacts with different behaviours:

- `MavenUtils`: uses m2e to resolve items, and is subject to the m2e preferences
- `DependencyResolver`: uses aether directly, using m2e's configurations as a base that we can override

And our library resolving infrastructure uses `MavenUtils`, whereas our `BuildPath` support uses the `DependencyResolver`. By using `DependencyResolver` everywhere, we can configure Aether to ignore the .lastUpdated files (`setUpdatePolicy(RepositoryPolicy.UPDATE_POLICY_*)`).

```
May 24, 2018 12:31:36 PM com.google.cloud.tools.eclipse.appengine.localserver.ServletClasspathProvider$1 onFailure
WARNING: Failed to resolve servlet APIs
java.util.concurrent.ExecutionException: org.eclipse.core.runtime.CoreException: Could not resolve artifact javax.servlet:servlet-api:jar:2.5
at com.google.common.util.concurrent.AbstractFuture.getDoneValue(AbstractFuture.java:502)
at com.google.common.util.concurrent.AbstractFuture.get(AbstractFuture.java:461)
at com.google.common.util.concurrent.AbstractFuture$TrustedFuture.get(AbstractFuture.java:78)
at com.google.common.util.concurrent.Uninterruptibles.getUninterruptibly(Uninterruptibles.java:142)
at com.google.common.cache.LocalCache$Segment.getAndRecordStats(LocalCache.java:2461)
at com.google.common.cache.LocalCache$Segment.loadSync(LocalCache.java:2425)
at com.google.common.cache.LocalCache$Segment.lockedGetOrLoad(LocalCache.java:2298)
at com.google.common.cache.LocalCache$Segment.get(LocalCache.java:2211)
at com.google.common.cache.LocalCache.get(LocalCache.java:4154)
at com.google.common.cache.LocalCache.getOrLoad(LocalCache.java:4158)
at com.google.common.cache.LocalCache$LocalLoadingCache.get(LocalCache.java:5147)
at com.google.cloud.tools.eclipse.appengine.libraries.repository.LibraryClasspathContainerResolverService.resolveLibraries(LibraryClasspathContainerResolverService.java:177)
at com.google.cloud.tools.eclipse.appengine.libraries.repository.LibraryClasspathContainerResolverService.lambda$0(LibraryClasspathContainerResolverService.java:168)
at com.google.cloud.tools.eclipse.util.jobs.PluggableJob.compute(PluggableJob.java:69)
at com.google.cloud.tools.eclipse.util.jobs.FuturisticJob.run(FuturisticJob.java:285)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:56)
Caused by: org.eclipse.core.runtime.CoreException: Could not resolve artifact javax.servlet:servlet-api:jar:2.5
at org.eclipse.m2e.core.internal.embedder.MavenImpl$5.call(MavenImpl.java:776)
at org.eclipse.m2e.core.internal.embedder.MavenImpl$5.call(MavenImpl.java:1)
at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeBare(MavenExecutionContext.java:177)
at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:112)
at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:99)
at org.eclipse.m2e.core.internal.embedder.MavenImpl.resolve(MavenImpl.java:743)
at org.eclipse.m2e.core.internal.embedder.MavenImpl.resolve(MavenImpl.java:720)
at com.google.cloud.tools.eclipse.util.MavenUtils.lambda$0(MavenUtils.java:98)
at com.google.cloud.tools.eclipse.util.MavenUtils.lambda$1(MavenUtils.java:124)
at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeBare(MavenExecutionContext.java:177)
at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:151)
at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:99)
at com.google.cloud.tools.eclipse.util.MavenUtils.runOperation(MavenUtils.java:120)
at com.google.cloud.tools.eclipse.util.MavenUtils.resolveArtifact(MavenUtils.java:93)
at com.google.cloud.tools.eclipse.appengine.libraries.repository.MavenHelper.resolveArtifact(MavenHelper.java:44)
at com.google.cloud.tools.eclipse.appengine.libraries.repository.M2RepositoryService.resolveArtifact(M2RepositoryService.java:50)
at com.google.cloud.tools.eclipse.appengine.libraries.repository.LibraryClasspathContainerResolverService.resolveLibraryFileAttachSourceSync(LibraryClasspathContainerResolverService.java:307)
at com.google.cloud.tools.eclipse.appengine.libraries.repository.LibraryClasspathContainerResolverService.access$0(LibraryClasspathContainerResolverService.java:304)
at com.google.cloud.tools.eclipse.appengine.libraries.repository.LibraryClasspathContainerResolverService$1.load(LibraryClasspathContainerResolverService.java:110)
at com.google.cloud.tools.eclipse.appengine.libraries.repository.LibraryClasspathContainerResolverService$1.load(LibraryClasspathContainerResolverService.java:1)
at com.google.common.cache.LocalCache$LoadingValueReference.loadFuture(LocalCache.java:3716)
at com.google.common.cache.LocalCache$Segment.loadSync(LocalCache.java:2424)
… 10 more
```