Fix Redis service to use the latest version and to work on OS X

Updated reference to Redis v 2.8.6.
Changed downloadPath to point to the new URL for Redis.
Placed a check to avoid recompiling Redis.
Added a chmod task to make mkreleasehdr.sh executable for make to work
on Mac OS X 10.9.1 with Cloudify 2.7.0 GA (build 5996). This should
work on other Unix platforms. Requires testing.