Apt cannot have 2 mirrors with the same content in 2 different files.
If a deployer has an apt mirror with mariadb (and others), the deployer
still need to add a repository, but will also need to define the
filename used, in order to avoid clashes.
This commit makes possible to decide the filename for the repo.
Change-Id: Ic83d464512f6f8697e520d79520dcf21370f8beb
Signed-off-by: Jean-Philippe Evrard <jean-philippe.evrard@rackspace.co.uk>