VCS: Use source() for file path where applicable

Task-number: QTCREATORBUG-9834

Change-Id: I5ee84593c56a0e3beaf20ef643b04d4de40c37f3
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
VCS: Support silent output on runVcs

Change-Id: If737b03f9d090076e9d739189479fb6725ae8856
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>