Clone VCS repositories for devserver users

Summary:
Commit 93a72bcf53c8 has introduced file provisionning for users,
but these files can also require software from known repositories.

Only git, hg and svn are supported, as the system wants to use a
salt.states.<chosen vcs>.latest state.

Test Plan: Tested on Ysul

Reviewers: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1404