Fix remounting overlay tests failure

The tests were running before boot complete but required
StorageManager to finish initialization before a package could be
installed.

This change makes the test wait for the device to be available by
using reboot(). Also remove code to retrieve resource value from
target APK and use "cmd overlay lookup" to see if the resources
are overlaid.

Bug: 147660952
Test: atest OverlayRemountedTest
Change-Id: I5929d3a57ad492ce0128b4a18e636ae96982bc62