Vagrantfile: Fix escaping of environment variables in dev vm bashrc initialization.

Previously, the hardcoded $PATH was ending up in the bashrc file.  The "$PATH" variable is now placed in the bashrc file, thus doing the more correct thing with chaining changes to that variable.

Signed-off-by: Eric Myhre <eric@flynn.io>
Merge pull request #553 from flynn/fix-vm-env-template-escaping

Vagrantfile: Fix escaping of environment variables in dev vm bashrc initialization