Revert "Removing exists action."

This reverts commit f3ecd40f14f5ebace24c98ef5b3542d56228c247.
Revert "Adding virtualenv to buildpack."

This reverts commit 88f875024f59f1bfd92fe9f4160cb0ae3e0486b3.
Revert "Add support for resetting virutalenv."

This reverts commit 87613f8befca43ab6b806b2fc189d90a88b06be6.