ACCUMULO-2015 clean up role files for standalone

Add checks for gc and tracers file existance in start-* scripts, since
these files are recommended but not required for cluster operation
Merge branch 1.4.5-SNAP into 1.5.1-SNAP (-sours)
ACCUMULO-2037 master is not fetching last location from the metadata table
Merge branch '1.4.5-SNAPSHOT' into 1.5.1-SNAPSHOT
ACCUMULO-2037 master is not fetching last location from the metadata table
Merge branch '1.6.0-SNAPSHOT'