"core": vbash should not modify $PATH
"core": vbash should not modify $PATH

This CL updates vbash so that it does not modify $PATH

Change-Id: I8fe1650a08df3b3501b90a70ff4b47b91fc96cae

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref