Cherry-pick from master: Fix issue #3324032:

(I forgot to commit this before the MR2 branch was made.)

It is possible to create an app that cannot...
...be uninstalled using device policy managers

Don't allow app switches while we are bringing up the confirmation
dialog.  This prevents the app from pushing us out of the intended
settings app flow.

Change-Id: Id670e231ac47346478d22a3f59bb4a44a68ef7b2