[#80253548]   Auto updates submodules only on Jenkins and only when permitted by a Jenkins environment flag setting

Assumptions for this PR from [Pivotal story](https://www.pivotaltracker.com/story/show/80253548):

Main requirements changes:

1.  No longer offer auto-update since this will be handled by the submodule developers.  I.e. if they update a submodule, then they are responsible for updating the relevant parent project SHAs.  This carries over even into Jenkins deployments, since Jenkins cannot assume submodule SHA configuration.
1.  @JamesLavin points out that turning this off risks going back to the development conditions that caused this feature to be generated in the first place.  The risk is that a parent project that hasn't updated a subproject SHA in a long time risks having lots of bugs caused when the submodule is updated for the parent.
1.  Hence, because we're not sure whether we want to keep auto-submodule SHA updating, there is now a Jenkins environment variable that determines whether this is performed.  See [wiki](https://github.com/hedgeyedev/hedgeye_utilities_for_jenkins/wiki/Whether-to-Auto-Update-Submodule-SHAs) for details
1.  No presumption of only `master` branch for submodules; submodules can have their own branches.