Fix VM-less builds.

This patch modifies Android.common_build.mk to avoid breaking the build
when trying to generate a system image that doesn't include a VM (which
is useful for low-level emulator feature testing, not general Android
development).

BUG=18581643

Change-Id: Ib75ebf14d3e9c8fc2ac591c7edd2ab4d6ff2ca89
1 file changed