CTS: Create test for DISALLOW_INSTALL_UNKNOWN_SOURCES

Added a new CTS app - PackageInstaller to test installing apk in a non
device owner package under policy restrictions

Note:
UserRestrictionActivity is copied from ManagedProfileTest

Bug: 18928535
Change-Id: I4fced5b345c4594009203681501ad84079dd3c61
16 files changed