ObsPy test suite on Docker images

This PR adds a couple of scripts and resources to test ObsPy on various Linux based operating systems using [Docker](http://www.docker.com).

It is pretty useful for **testing the current state (branch, tag, uncommited changes, ...) of the repository on a machine** on different operating system and various versions of Python and ObsPy's dependencies. This eases testing for certain classes of bugs like in #823.

It currently has image receipts for the following operating systems: CentOS 6, Debian (Squeeze, Wheezy, and Jessie), Fedora 20, and openSUSE 13.1; all in 64 bit. It is very easy to add additional systems which we should probably do.

The test script is still in a fairly basic state and could be extended in a number of ways but it works well enough.

For more details, please see the readme:
https://github.com/krischer/obspy/tree/docker_tests/misc/docker_tests