updates provisioning, adds peer 2 canfigs

- provisioning checks if the expected gnu net src folders exists before downloading & installing
- adds GNUNET_PREFIX to vagrant bashrc if not there already
Merge pull request #7 from NemoOudeis/develop

updates provisioning, adds peer 2 configs
feat(testbed): The code for the testbed example from the C tutorial

Does not seem to work because of some gnunet missconfiguration. But at least it
is already compiling.

WIP for #3