Starting ImageScaler tmp dir move from /a to /tmp

ImageMagick temp directory currently resides in /a/magick-tmp which
collides with other uses of /a. This is the first bit of a move which
will have the new temp directory in /tmp/magick-tmp; but before we
must walk the config over.

so A) Apply this and wait for cluster to pick it up
B) effect MW config change of wgImageMagickTempDir
C) Remove the /a requirements from puppet
D) manually go thru and remove the /a directories on the image scalers

Change-Id: I88554cc9cd4b29e664757e1b4001448c6f20cad9
Merge "Starting ImageScaler tmp dir move from /a to /tmp" into production