qemu: snapshot: Don't attempt to resume cpus if they were not paused

External disk-only snapshots with recent enough qemu don't require
libvirt to pause the VM. The logic determining when to resume cpus was
slightly flawed and attempted to resume them even if they were not
paused by the snapshot code. This normally was not a problem, but with
locking enabled the code would attempt to acquire the lock twice.

The fallout of this bug would be a error from the API, but the actual
snapshot being created. The bug was introduced with when adding support
for external snapshots with memory (checkpoints) in commit f569b87f.

Resolves problems described by:
https://bugzilla.redhat.com/show_bug.cgi?id=1403691

src/qemu/qemu_driver.c

@@ -14472,8 +14472,6 @@ qemuDomainSnapshotCreateActiveExternal(virConnectPtr conn,
     if (virDomainObjGetState(vm, NULL) == VIR_DOMAIN_PMSUSPENDED) {
         pmsuspended = true;
     } else if (virDomainObjGetState(vm, NULL) == VIR_DOMAIN_RUNNING) {
-        resume = true;
-
         /* For external checkpoints (those with memory), the guest
          * must pause (either by libvirt up front, or by qemu after
          * _LIVE converges).  For disk-only snapshots with multiple
@@ -14496,6 +14494,8 @@ qemuDomainSnapshotCreateActiveExternal(virConnectPtr conn,
                                _("guest unexpectedly quit"));
                 goto cleanup;
             }
+
+            resume = true;
         }
     }