Fix git dependencies with salt 3005.5+ and 3006.6+

[sblaisot]

Salt 3005.5 and salt 3006.6 introduced a fix for a CVE that refuse to serve files outside of files_root

When using git dependencies, they are cloned outside of files_root and we used to make a symlink from files_root to the dependencies formulas.

This pull request replace the symlink witth a hard copy of the dependencies inside files_root to make dependencies work under salt 3005.5+ and 306.6+

This fixes #348