Add CTS test for startActivity vs exported

Specifically, require that if startActivity() is called for an activity
component that is not exported, a permission denial is thrown.

The new hostsidetests/os umbrella is intended, going forward, as a place
to put other core OS test content that requires being driven from the
host side.

Bug 23223804

Change-Id: I498a08deb66f8bdb55bc1b19e5cc3f93a0cfb494
7 files changed