Always launch BlockedAppStreamingActivity as SYSTEM user

With different user the activity will be blocked which results in
infinite recursive loop.

Bug: 328298904
Test: Manually reproduced bug with Exo and tested the bugfix
Test: atest ActivityBlockingTest
Change-Id: I36761e7104418d41d22f97f82cef336833709060
(cherry picked from commit f44a53f9)