[zorg] Add optional checkAll step to Polly buildbot
This step does "make check-all" and can be enabled by checkAll (defaults to
false in which case only "make check-polly" is run).
Reviewers: mgrang, zinob, gkistanova, vleschuk, grosser, bollu
Reviewed By: grosser
Differential Revision: https://reviews.llvm.org/D36277