RI-179 Make agent work on CentOS 7

CentOS 7 is pretty new, but it uses Python 2.7 and does not have any Python paths in common with 2.6.  So, post-install, we will check for the presence of a python2.7 lib directory and symlink it there.

Only the 64 bit version is available (as far as I can tell), so that's what I manually tested this on.  There are a few Vagrant images, but none of them work, so I was unable to add integration tests for now, until CentOS 7 is a bit more mainstream.

Do you mind taking a look at this @divtxt ?