Allow resubmiting the very same module build in case it results in new MSE build.
    
    This is needed for Fedora branching, but it is generally useful.
    
    For example, there is a module buildrequiring "platform:[]". In the time
    this module has been built, only platform:f29 existed, so it has been built
    just against platform:f29.
    
    After a while, the platform:f30 is released and the maintainer needs
    to rebuild the module against platform:f30. Right now, he needs to create
    new commit in the module and submit the build, but this will result in useless
    rebuild of the module also against platform:f29.
    
    In this commit, MBS allows to resubmit the module build in a case
    there are new MSE builds to build. MBS will send all the module builds
    back to the user - so the existing builds will be already marked as
    "ready" and the newly submitted builds will have the "init" state in
    the REST API response.
    
    However, in case when there are no new MSE builds to build, MBS still
    sends back the Conflict error as it used to. This is done for backwards
    compatibility and also to not confuse the users in case when no new build
    has been submitted.