qemu: don't hold both jobs for suspend

qemu: don't hold both jobs for suspend

We have to assume that the guest agent may be malicious so we don't want
to allow any agent queries to block any other libvirt API. By holding a
monitor job while we're querying the agent, we open ourselves up to a
DoS.

So split the function up a bit to only hold the monitor job while
querying qemu for whether the domain supports suspend. Then acquire only
an agent job while issuing the agent suspend command.

Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com>
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>