In QEMUMonitorProtocol, commit e9d17b68 removed the __sockfile creation
from __negotiate_capabilities(), which breaks _accept().  This causes
failures in qemu-io python based tests (i.e. tests 030 and 040).

This patch creates the sockfile in __accept() as well.
Signed-off-by: NJeff Cody <jcody@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Acked-by: NLuiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>