tests: start/stop an event thread for QEMU monitor/agent tests
tests: start/stop an event thread for QEMU monitor/agent tests

Tests which are using the QEMU monitor / agent need to have an
event thread running a private GMainContext.

There is already a thread running the main libvirt event loop
but this can't be eliminated yet as it is used for more than
just the monitor client I/O.

Reviewed-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>
Signed-off-by: Daniel P. Berrangé <bb938cf255e055ff3507f2627d214e8e62118fcf@redhat.com>

crobinso/libvirt,olafhering/libvirt,libvirt/libvirt,crobinso/libvirt,libvirt/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,jfehlig/libvirt,jardasgit/libvirt,crobinso/libvirt,jardasgit/libvirt,jfehlig/libvirt,nertpinx/libvirt,jardasgit/libvirt,zippy2/libvirt,crobinso/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,zippy2/libvirt,olafhering/libvirt,nertpinx/libvirt,nertpinx/libvirt,jardasgit/libvirt,olafhering/libvirt,libvirt/libvirt,zippy2/libvirt,jfehlig/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,zippy2/libvirt,fabianfreyer/libvirt,olafhering/libvirt,libvirt/libvirt