Add recursive submodule setting for Git repositories

[mspaulding06]

This is a setting that I've found can be necessary for repositories that have broken .gitmodules files in them. This is necessary for a related PR I am submitting for the glide tool as it fails to check out the git2go project. I will explain further the reasoning in that PR.

For this PR I have just added an option that can be set that only affects Git repositories and just prevents use of the --recursive option if the Recursive field is set to false on the repo struct.

[AppVeyorBot]

:white_check_mark: Build vcs build-84.master completed (commit https://github.com/Masterminds/vcs/commit/56f3dc1713 by @mspaulding06)

[mattfarina]

For reference, the PR for glide is at Masterminds/glide#920