fix(instances): the quota counts queued clones and pending values

A user's quota counted each VM's running vCPUs, memory and disks, so a
larger value set for the VM's next start was not counted, and a clone
counted only once its VM was recorded, so a user could queue clones
past the quota. Now:

- Each VM counts the larger of its running and its next-start values.
- A clone job counts as one VM with the source's persistent vCPUs,
  memory and disk size, which its plan stores, from its admission until
  its VM is recorded; a failed, cancelled or resolved job no longer
  counts. The clone's VM and its owner are recorded in one transaction,
  so the quota counts either the job or the VM, never neither.
- The quota reads each VM's definition once (cached_reads).

vrtManager/instance.py

@@ -713,8 +713,8 @@ class wvmInstance(wvmConnect):
 
         return vcpus
 
-    def get_memory(self):
-        mem = util.get_xml_path(self._XMLDesc(0), "/domain/memory")
+    def get_memory(self, config=False):
+        mem = util.get_xml_path(self._XMLDesc(PERSISTENT_XML if config else 0), "/domain/memory")
         return int(mem) // 1024
 
     def get_cur_memory(self):