Update global_variables to use the compile bots (and housekeeper) in us-central2-b
Update global_variables to use the compile bots (and housekeeper) in us-central2-b

BUG=skia:2323
NOTREECHECKS=true
R=borenet@google.com

Author: rmistry@google.com

Review URL: https://codereview.chromium.org/210293002

Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot,Tiger66639/skia-buildbot,google/skia-buildbot,google/skia-buildbot,Tiger66639/skia-buildbot