Use Mockito Kotlin for SpaPrivilegedLibTests

Which has better support for Kotlin unit test.

Also specific Context.RECEIVER_NOT_EXPORTED for registerReceiverAsUser,
which is an Android U requirement.

Bug: 289155281
Test: manual - on Settings All Apps page
Test: unit test
Change-Id: I9264e7d61e4883d3db8212dbc9089924eb8e577f