[READ CAREFULLY] User switching and umask setting does not belong in VT

This should have been done quite a while ago, but I could only get to this now.

I'm submitting this against 2014.7 so that we don't have to deprecate this previous and undesirable behavior.
The reason why I ask you to read carefully is because this won't be tested in another RC since the .7 final might be close, however, this change should not break anything as it simply switches the previous behavior to the right place, out of VT.

The VT "behaviour" should be as close to subprocess as possible and this commit reverts the "behavior" breakage introduced.