MSIM: Fix crash during set subscription.

After setting subscription, configuration change is triggered
due to MCC-MNC values getting updated based on the sim. This
causes SetSubscription activity to be destroyed and re launched,
causing the AlertDialog window to be leaked from the activity.
Dismiss any dialogs displayed in onPause() to fix this.

Change-Id: I7b75a1bf69ca45053b26fee38649f4a0077351c9
CRs-Fixed: 631176