GitLab

Verifies that each user has its own isolated emulated storage, minus
shared storage for OBB files.  Also tests to verify that legacy
filesystem paths like "/sdcard" continue working.

Adds early support for multi-user CTS tests, should eventually be
moved into ITestDevice and RemoteAndroidTestRunner.

Bug: 7048947
Change-Id: I0573b9236b267ab798676926910ec4e1890fe7cb