daemon: Raise an error if 'max_workers' < 1 in libvirtd.conf

daemon: Raise an error if 'max_workers' < 1 in libvirtd.conf

Hypervisor drivers (e.g. QEMU) assume that they run in a separate
thread from the main event loop thread otherwise deadlocks can
occur. Therefore let's report an error if max_workers < 1 is set in
the libvirtd configuration file.

Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Reviewed-by: Boris Fiuczynski <fiuczy@linux.ibm.com>
Reviewed-by: Bjoern Walk <bwalk@linux.ibm.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>