Add 'sha1' to env fallbacks
Add 'sha1' to env fallbacks

Used by spark build and possibly others later on.

mesosphere/dcos-commons,tobilg/dcos-commons,tobilg/dcos-commons,comptelfwd/dcos-commons,adragomir/dcos-commons,tobilg/dcos-commons,tobilg/dcos-commons,comptelfwd/dcos-commons,comptelfwd/dcos-commons,mesosphere/dcos-commons,adragomir/dcos-commons,mesosphere/dcos-commons,vishnu2kmohan/dcos-commons,adragomir/dcos-commons,vishnu2kmohan/dcos-commons,mesosphere/dcos-commons,vishnu2kmohan/dcos-commons,adragomir/dcos-commons,tobilg/dcos-commons,mesosphere/dcos-commons,comptelfwd/dcos-commons,comptelfwd/dcos-commons,vishnu2kmohan/dcos-commons,vishnu2kmohan/dcos-commons,adragomir/dcos-commons,comptelfwd/dcos-commons