microdroid_manager: allow to read dm_device

Microdroid_manager should verify payloads(APK/APEXes). APK is mounted to
dm_device first and then verified. So, microdroid_manager needs to read
it.

Bug: 190343842
Test: MicrodroidHostTestCases
Change-Id: I530fb8d2394952486f0bad7fb3bed770611cd311
1 file changed