add python to brillo eng builds

We need this to run autotest tests.

The fs_config hack is a bit ugly, but it's just enough to unblock the
autotest guys.  We'll want to investigate this on a larger scale.

BUG=b:26861037
TEST=brilloemulator x86_64 eng boots and `python` works

Change-Id: I54ef7fec8556d7d4c140b46f756e01982f55a3e2
2 files changed