(MODULES-1571) Big refactor of `git_version`
(MODULES-1571) Big refactor of `git_version`

Biggest change is it now just the version number not the whole string.

Before:
`facter git_version #=> 'git version 2.1.2'`
After:
`facter git_version #=> '2.1.2'`

It also now uses the Facter::Util::Resolution.exec so we can mock it out easier in specs
johnduarte/puppetlabs-git,johnduarte/puppetlabs-git,gwdg/puppetlabs-git,mhaskel/puppetlabs-git,pagemachine/puppetlabs-git,pagemachine/puppetlabs-git,puppetlabs/puppetlabs-git,mhaskel/puppetlabs-git,patrickkelso/puppetlabs-git,michaeldfallen/puppetlabs-git,patrickkelso/puppetlabs-git,mbrodala/puppetlabs-git,redhat-cip/puppetlabs-git,mbrodala/puppetlabs-git,michaeldfallen/puppetlabs-git,gwdg/puppetlabs-git,redhat-cip/puppetlabs-git,puppetlabs/puppetlabs-git