Remove centos7-vagrant submodule from the repo

[dirgim]

Remove centos7-vagrant submodule from the repo to fix cloning problems.

[skatlapa]

@dirgim Hey, the error for y'day was for submodules not retrieved while cloning. So we can do two things:

1. Remove the submodules, which this PR did. And removing works perfectly if the submodules aren't needed(not sure if they're needed by any team).

2. To get the submodules we need to clone the repo recursively, so I added the checkout stage in this PR[1]. We can check my cherrypicking the patch and try cloning, but either ways, I think we will need a checkout stage anyways(re this PR for now I can disable the parameter "recursiveSubmodules" if submodules are not needed). THis basically does "git clone --recursive"

@arilivigni I guess this also answers the question in the PR[1]. @joejstuart any thoughts?

[1] - https://github.com/CentOS-PaaS-SIG/contra-env-setup/pull/130/files