android.system.virtualmachine is added as the client-side API for the
controlling of virtual machines. This change doesn't add any new API.
It adds an empty library to the existing framework.
Bug: 183496040
Test: atest MicrodroidHostTestCases
Change-Id: I9c52dfaf7e33137e5e3d6c587b5cc3932f667025
Jiyong Park