engine: Add job subject entity when adding job from cli

When creating a job for a gluster task detected from
cli, the job subject entity table needs to be populated as
well. This is needed for the gluster_task_steps view to
pick the correct entries.

Also implemented toString() for GlusterAsyncTask

Change-Id: I7996c5b2c52f276f40777fa485cf1a70ba76f381
Bug-Url: https://bugzilla.redhat.com/1040959
Signed-off-by: Sahina Bose <sabose@redhat.com>