MasterClear: fix FRP wipe crash

Requesting setRequestedOrientation() right after showing a custom dialog
in a DialogFragment does not play nice. It forces the activity to be
recreated instantly, so when the task finishes, there original activity
the AsyncTask is tied to is no longer valid.

However, if we let fragment manager keep track of all the dialogs, it
doesn't break the expected behavior.

REF: CYNGNOS-427
Change-Id: I0609816182a6b5319d2a88ff0075d53e3c2fed16
Signed-off-by: Roman Birg <roman@cyngn.com>