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
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:f44a53f962abc8af48d875c85da8a69eb3dfa23c)
Merged-In: I36761e7104418d41d22f97f82cef336833709060
Change-Id: I36761e7104418d41d22f97f82cef336833709060