ACCUMULO-1925 ensure system tests respect ACCUMULO_CONF_DIR.

(cherry-picked from commit 422aaaa7c35de07c280d496e489fbab541edeea3)

Reason: Tests
Author: Ryan Fishel <ryan.fishel@cloudera.com>
Author: John Vines <jvines@gmail.com>

Conflicts:
	test/system/auto/TestUtils.py
	test/system/continuous/start-stats.sh

Signed-off-by: Eric Newton <eric.newton@gmail.com>
Merge branch '1.6.0-SNAPSHOT'