Fix jcloudsByon: don’t do machine.setParent(null)

- previously the FixedListMachineProvisioningLocation only took
  machines that did not already have a parent.
- that meant jcloudsByon needed to “unparent” the rebound jclouds 
  machine, so it could be added to the FLMPL.
- however, setting parent to null “unmanaged” the location, which
  causes problems when it then becomes managed again.
avoid NPE in AbstractLocation if creationTimeUtc null

- happens if you unmanaged and then remanage an entity.
- the old creationTimeUtc will have been deleted from storage so will
  be null, so doing `long l = createTimeUtc.get()` NPEs
Merge pull request #1432 from aledsage/fix/jcloudsByon

Fix jcloudsByon