Wait for name resolutions to complete before shutting down iomgr.

This at least avoids crashing when shutting down during name resolution.
There is still a memory leak to track down before I add a test that exposes
this.

This CL also makes some tiny cleanups and debuggability improvements.
	Change on 2014/12/11 by ctiller <ctiller@google.com>
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=81882486