qemu: bulk stats: extend internal collection API

qemu: bulk stats: extend internal collection API

Future patches which will implement more bulk stats groups for QEMU will
need to access the connection object.

To accommodate that, a few changes are needed:

* enrich internal prototype to pass qemu driver object

* add per-group flag to mark if one collector needs monitor access or not

* If at least one collector of the requested stats needs monitor access
  we must start a query job for each domain.  The specific collectors
  will run nested monitor jobs inside that.

* If the job can't be acquired we pass flags to the collector so
  specific collectors that need monitor access can be skipped in order
  to gather as much data as is possible.

Signed-off-by: Francesco Romani <fromani@redhat.com>
Signed-off-by: Peter Krempa <pkrempa@redhat.com>