unify resource scanner's Run, ScanFromVersion, and Scan methods
unify resource scanner's Run, ScanFromVersion, and Scan methods

Signed-off-by: Joris Melchior <11bab9258783d999ff385b9a7a8380b7472aa4eb@pivotal.io>

concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse