servo-linux3 no longer has salt installed and has incompatible packages present

[jdm]

The contents of /var/log/dpkg.log show salt being installed on 5/12 when I was setting up the new build machine. On 5/17 it shows an updated version of pip being installed (as a result of the debugging in servo/servo#20813), which caused salt to be uninstalled because python was upgraded in an incompatible way. We're now in the situation where reinstalling salt requires the python-requests package, which requires python-urllib3, but the installed version of libpython2.7 prevents installing the version of python-urllib3 that is available:

 libpython2.7-stdlib:amd64 (2.7.14-2ubuntu1~14.04.york1) breaks python-urllib3 (<< 1.9.1-3) and is installed.

Until this is resolved, we can't communicate with servo-linux3 with salt.

[jdm]

I tried recreating servo-linux3 from scratch and ran into the exact same problem as servo/servo#20813. I'm a bit terrified now; I'm just shutting the new builder down rather than continuing to dig into it right now.