default user for verifying karaf log file should be ${CONTROLLER_USER}

default user for verifying karaf log file should be ${CONTROLLER_USER}

hopefully we will end up using more descriptive variables like
ODLVM1_USER, but for now CONTROLLER_USER is avaiable.  This patch
fixes a bug, where the default user for "Run Command On Remote
System" has it's default user as ${MININET_USER}.  If the
given environment has different users for the mininet and controller
VM, this keyword "Check Karaf Log File Does Not Have Messages"
ended up using ${MININET_USER} which is obviously wrong since
the karaf.log file is always going to be on the controller.

small bug, but hit me locally.

Change-Id: Id9ef26a1ac691a814e6165bd55cbf69edc3e325f
Signed-off-by: Jamo Luhrsen <jluhrsen@redhat.com>