Add missing regex to backup manager
Add missing regex to backup manager

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/10901/diffs
introduced a new naming scheme for backups, but the code which
cleans up old backups wasn't updated accordingly. In order to
maintain backward compatibility, we need to account for 3 naming
schemes.

stoplightio/gitlabhq,axilleas/gitlabhq,iiet/iiet-git,jirutka/gitlabhq,axilleas/gitlabhq,iiet/iiet-git,mmkassem/gitlabhq,dreampet/gitlab,t-zuehlsdorff/gitlabhq,mmkassem/gitlabhq,iiet/iiet-git,jirutka/gitlabhq,stoplightio/gitlabhq,jirutka/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq,iiet/iiet-git,stoplightio/gitlabhq,dplarson/gitlabhq,dplarson/gitlabhq,axilleas/gitlabhq,axilleas/gitlabhq,t-zuehlsdorff/gitlabhq,dreampet/gitlab,t-zuehlsdorff/gitlabhq,t-zuehlsdorff/gitlabhq,dreampet/gitlab,dreampet/gitlab,mmkassem/gitlabhq,dplarson/gitlabhq,jirutka/gitlabhq,dplarson/gitlabhq