Outside blockjob.c, block_job_unref is only used when a block job fails
to start, and block_job_ref is not used at all.  The reference counting
thus is pretty well hidden.  Introduce a separate function to be used
by block jobs; because block_job_ref and block_job_unref now become
static, move them earlier in blockjob.c.
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NJohn Snow <jsnow@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: NJeff Cody <jcody@redhat.com>
Message-id: 20170508141310.8674-4-pbonzini@redhat.com
Signed-off-by: NJeff Cody <jcody@redhat.com>