ACCUMULO-3341 Make deletetable remove any tables in the accumulo namespace before attempting deletion.

Also fixed the test package from 'command' to 'commands'.
Merge branch '1.6'

Conflicts:
	core/src/test/java/org/apache/accumulo/core/util/shell/command/FormatterCommandTest.java
	core/src/test/java/org/apache/accumulo/core/util/shell/command/HistoryCommandTest.java
	core/src/test/java/org/apache/accumulo/core/util/shell/commands/FormatterCommandTest.java
	core/src/test/java/org/apache/accumulo/core/util/shell/commands/HistoryCommandTest.java
	shell/src/main/java/org/apache/accumulo/shell/commands/DeleteTableCommand.java
	shell/src/test/java/org/apache/accumulo/shell/command/FormatterCommandTest.java
	shell/src/test/java/org/apache/accumulo/shell/command/HistoryCommandTest.java
ACCUMULO-3347 Log a message when a sesion is torn down due to it being idle or not accessed.
Merge branch '1.6'

Conflicts:
	server/tserver/src/main/java/org/apache/accumulo/tserver/TabletServer.java
WIP