Added a script to build Mesos docker image.
Added a script to build Mesos docker image.

This script leverages the packaging scripts to build the RPM first, and
then generate the Mesos docker image by installing the Mesos RPM. This
results in smaller Mesos docker image.

This script can be run on both Linux or OSX. You just need to have
Docker installed.

Currently, the script will build a Mesos docker image from the current
head. Future work will make it work for building a specific tag or sha.

Review: https://reviews.apache.org/r/63939/

dforsyth/mesos,reneploetz/mesos,dforsyth/mesos,kaysoky/mesos,abudnik/mesos,jpeach/mesos,andschwa/mesos,gsantovena/mesos,asamerh4/mesos,kaysoky/mesos,jpeach/mesos,abudnik/mesos,andschwa/mesos,asamerh4/mesos,reneploetz/mesos,asamerh4/mesos,chhsia0/mesos,kaysoky/mesos,Gilbert88/mesos,andschwa/mesos,gsantovena/mesos,andschwa/mesos,asamerh4/mesos,chhsia0/mesos,jpeach/mesos,dforsyth/mesos,kaysoky/mesos,reneploetz/mesos,reneploetz/mesos,Gilbert88/mesos,Gilbert88/mesos,jpeach/mesos,gsantovena/mesos,andschwa/mesos,dforsyth/mesos,chhsia0/mesos,jpeach/mesos,asamerh4/mesos,gsantovena/mesos,asamerh4/mesos,Gilbert88/mesos,abudnik/mesos,Gilbert88/mesos,dforsyth/mesos,andschwa/mesos,chhsia0/mesos,asamerh4/mesos,kaysoky/mesos,chhsia0/mesos,Gilbert88/mesos,jpeach/mesos,chhsia0/mesos,abudnik/mesos,Gilbert88/mesos,abudnik/mesos,chhsia0/mesos,dforsyth/mesos,reneploetz/mesos,kaysoky/mesos,abudnik/mesos,gsantovena/mesos,gsantovena/mesos,dforsyth/mesos,reneploetz/mesos,reneploetz/mesos,abudnik/mesos,andschwa/mesos,kaysoky/mesos,jpeach/mesos,gsantovena/mesos