Don't set DPM password expiration unless it has changed

* Because we push the expiration value frequently (not only when
  policies change, but also after alerting the user to change his
  settings), we're pushing this value further and further into
  the future.
* In the referenced bug, the data IS being deleted, but then the
  expiration is pushed out, putting us back into compliance with
  policies (wrongly), which leads to the data syncing right back
  again
* The fix is to only push the expiration when it has changed; the
  fix is trivial

Bug: 6813598
Change-Id: Ibd238813e3f2f25e7f1f176c31cb31d00874dba6
merge in jb-mr0-release history after reset to jb-dev
Merge android-4.1.2_r1