labs: osbashauto exit on script error

Make osbashout abort if a client-side scripts returns an error; use a
file named error in the status directory to signal the problem and to
store the name of the offending script for use by Windows batch scripts.

Have osbash.sh and the Windows batch scripts exit when an error file
appears.

Change-Id: I6722e75c9c23b99e5ed25b00429026c2e0ff6a12