base

Add device-owner based setting of global proxy.

Re-hide the setGlobalProxy on the ConnectivityManager as it requires
CONNECTIVITY_INTERNAL.  Instead add a function to the DevicePolicyManager
to set the global proxy, that can only be called by the device owner.

Change-Id: I9ffb2cc4f30a6dc9b868d86f056e1fbd512d8dfc