clean up MockDirectoryWrapper.close() [LUCENE-4058]

background on #5119.

MockDirectoryWrapper.close() should always try to close its wrapped resources in a finally block, even if its going to throw exceptions.

Otherwise if lots of tests fail, resources could pile up (e.g. RAMDirs).

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Migrated from [LUCENE-4058](https://issues.apache.org/jira/browse/LUCENE-4058) by Robert Muir (@rmuir), updated Jul 06 2012

Locate MockDirectoryWrapper.close() and read the background in #5119 to understand the wrapped resources involved. Done means close() still attempts to close those resources in a finally block when an exception is thrown; run the existing tests covering MockDirectoryWrapper and resource cleanup.

Written by the indexing model from the issue text.