Memoize GitlabShellAdapter for performance and ease of testing
Memoize GitlabShellAdapter for performance and ease of testing

Port of https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/3463#note_47990536

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