ACCUMULO-2382 make agitation work with a non-default CONTINUOUS_CONF_DIR.

* Change start-agitator to use inferred installation directory instead of passed in conf dir.
* Ensure tserver and master agitator default ot ACCUMULO_HOME if present, so that starting all as root works.
Merge branch '1.5.2-SNAPSHOT' into 1.6.0-SNAPSHOT
ACCUMULO-2382 make continuous ingest test mapreduce jobs work with non-default CONTINUOUS_CONF_DIR