core : Add queuing capabilities to ThreadPoolUtil

Since some customers get out of threads execptions, this patch will add a queuing
capability to our default thread pool.

Change-Id: Iab7054c77c9ec8795de85df0fd45dde06c18ab1e
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1007393
Signed-off-by: lzelkha@redhat.com <liran.zelkha@gmail.com>