Stabilize the result of stdlib's keys function

The stdlib keys function returns the keys of a puppet hash.
Unfortunately puppet hashes are not consistent in every run and as a
result the keys function return value maybe different in every
subsequent invocation. Sorting the result right before returning it
solves this

Change-Id: I3a5b3e4b069cfc4a8cd0739a27a16fc8ac8c967d
Merge "Stabilize the result of stdlib's keys function" into production