ACCUMULO-1858 Backport ZooKeeper clean up to 1.4 and 1.5.

Fix cherry picks two commits:

ACCUMULO-1379 - Adding close() to Instance to assist in freeing up resources

(cherry picked from commit 7da1164d87227960d3e0cfc841f753067e2c0304)

Reason: bugfix
Author: John Vines <jvines@gmail.com>

Differs from original by path changes and leaving out ConditionalWriterTest, which is only in 1.6.0+

----

ACCUMULO-1379 Fix edge cases if error in closing ZooKeeperInstance

(cherry picked from commit 3f6c66ede52cb1fb5a122d7bad06d7978ff0a671)

Reason: bugfix
Author: Christopher Tubbs <ctubbsii@apache.org>

Signed-off-by: Bill Slacum <ujustgotbilld@apache.org>