qemu: Obtain reference on monConfig

qemu: Obtain reference on monConfig

Because we allow a QEMU_JOB_DESTROY to occur while we're starting
up and we drop the @vm lock prior to qemuMonitorOpen, it's possible
that a domain destroy operation "wins" the race, calls qemuProcessStop
which will free and reinitialize priv->monConfig. Depending on the
exact timing either qemuMonitorOpen will be passed a NULL @config
variable or it will be using free'd (and possibly reclaimed) memory
as the @config parameter - neither of which is good.

Resolve this by localizing the @monConfig, taking an extra reference,
and then once we get the @vm lock again removing our reference since
we are done with it.

Signed-off-by: John Ferlan <jferlan@redhat.com>
Reviewed-by: Marc Hartmayer <mhartmay@linux.vnet.ibm.com>