cluster/afr: Add foreground self-heal launch capability through lookup

Also renamed allow-sh-for-running-transaction -> attempt-self-heal

Change-Id: I134cc79e663b532e625ffc342c59e49e71644ab3
BUG: 1039544
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/6463
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: venkatesh somyajulu <vsomyaju@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>