CI for PBSPro using Docker

[guillaumeeb]

This issue is derived from #2. The goal is to add some CI configuration for testing PBSCluster on a toy dockerized cluster. See work done in #23 and #27 for SGE.

Some useful comments:
#2 (comment)

#2 (comment)

[guillaumeeb]

I'm still up for this one, but I've not really worked on it so far. Hopefully in the next few weeks, but if someone has more bandwidth and is willing to try, that's fine with me.