Fix secondary user test for VirtualDevice

- Clear binder identity before calling getPackageUid
- VirtualDeviceImpl uses the owner's user ID to create its Context
- For virtual camera, create a different CameraAccessController for each
  user

Fixes: 218790107
Test: (On secondary user) atest CtsVirtualDevicesTestCases
Change-Id: I63027ab58854f11faa4e2b20da202886dd10d2f3