Address some warnings.

Conflicts:
	community/kernel/src/main/java/org/neo4j/kernel/impl/util/FileUtils.java
Better error reporting if recursive directory deletes fail.

o Although it threw an IOException if the delete failed, we didn't get
  any information about why, because #deleteFile() itself doesn't throw
  an exception.

o We would like to get better reporting to help diagnose flaky tests.

o I am reluctant to change FileUtils#deleteFile() itself to throw an
  exception instead of returning a boolean because it is so widely used.

Conflicts:
	community/kernel/src/main/java/org/neo4j/kernel/impl/util/FileUtils.java
Reintroduce special handling for Windows' inability to release memory-mapped files.
Reintroduce deletion of test directories for passing tests.

This now includes a workaround for the problem that we see when deleting
test directories on Windows for tests that memory-map files.
Merge pull request #2312 from benbc/2.0-delete-data-for-passing-tests

2.0 delete data for passing tests