ACCUMULO-2865 Add ZooCacheTest

This adds a unit test for ZooCache. ZooCache itself was only changed slightly, with the
addition of methods to check if information was cached and improvements to its comments.
Merge branch '1.6.1-SNAPSHOT'
ACCUMULO-2803 Agitator: Independent Tablet Server and Datanode Min/Max Kill Values
Merge branch '1.5.2-SNAPSHOT' into 1.6.1-SNAPSHOT
ACCUMULO-2869 Ensure that the proper property is set for the index block size.
Merge branch '1.6.1-SNAPSHOT'

Conflicts:
	server/tserver/src/main/java/org/apache/accumulo/tserver/tablet/Tablet.java
Merge branch '1.6.1-SNAPSHOT' of https://git-wip-us.apache.org/repos/asf/accumulo into 1.6.1-SNAPSHOT
ACCUMULO-2874 update the docs to match the actual API
ACCUMULO-1919 Size of visibility cache in AccumuloFileOutputFormat should be configurable.

Signed-off-by: Josh Elser <elserj@apache.org>
ACCUMULO-2874 update the docs to match the actual API
Merge branch '1.6.1-SNAPSHOT'
ACCUMULO-2874 update the docs to match the actual API
Merge branch '1.6.1-SNAPSHOT' of https://git-wip-us.apache.org/repos/asf/accumulo into 1.6.1-SNAPSHOT
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/accumulo
ACCUMULO-2862 stop re-throwing CompactionInteruptedException, wrote a test to verify that splits interrupt major compactions
ACCUMULO-1919 add missing import
ACCUMUMLO-2255 more little cleanups and class extractions
ACCUMULO-2753 used TServerInstance to encode mutations
ACCUMULO-2876 Use site config to configure default VolumeManagerImpl

This changes VolumeManagerImpl.get() to use the site configuration instead of the
ZooKeeper-based system configuration. This seems to align better with what is intended,
and it also eliminates the risk of an infinite loop, where the system configuration
requires an HdfsZooInstance instance ID, which requires a volume manager.
Merge branch '1.6.1-SNAPSHOT'