Implement permission check for virtualizationservice

For the service to be able to check permission, the AIDL interface is
exported to the virt APEX where virtualizationservice is in.

In addition, the VM permissions are granted to shell so that developers
can use the 'vm' tool on the shell.

Bug: 168588769
Test: /apex/com.android.virt/bin/vm run-app --log /dev/null
/data/local/tmp/virt/MicrodroidDemoApp.apk
/data/local/tmp/virt/MicrodroidDemoApp.apk.idsig assets/vm_config.json

Change-Id: I00db58ba9cef3b83f43db68ef86f062b59a0e6e1