CBD-1425:  initial capture of buildbot steps

There is an echo statement for each step from a 3.0.0 build,
implying that each step has been re-created here, but this
script differs from the buildbot job in these ways:

 - downloads current.xml posted by repo job
 - commented out manifest and override args to make
 - only building one edition
 - not all post-build steps implemented

Change-Id: I735b63bb8369738885eb266abb843c878871f52e
use:  server_macosx_build.sh voltron_branch release build_number edition manifest
Reviewed-on: http://review.couchbase.org/40385
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>