Use branch_exists? to check branches
Use branch_exists? to check branches

Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7237#note_19747922

dreampet/gitlab,jirutka/gitlabhq,axilleas/gitlabhq,htve/GitlabForChinese,htve/GitlabForChinese,axilleas/gitlabhq,darkrasid/gitlabhq,axilleas/gitlabhq,stoplightio/gitlabhq,openwide-java/gitlabhq,darkrasid/gitlabhq,dreampet/gitlab,LUMC/gitlabhq,dplarson/gitlabhq,t-zuehlsdorff/gitlabhq,openwide-java/gitlabhq,dplarson/gitlabhq,stoplightio/gitlabhq,iiet/iiet-git,t-zuehlsdorff/gitlabhq,mmkassem/gitlabhq,iiet/iiet-git,darkrasid/gitlabhq,jirutka/gitlabhq,openwide-java/gitlabhq,LUMC/gitlabhq,openwide-java/gitlabhq,stoplightio/gitlabhq,axilleas/gitlabhq,mmkassem/gitlabhq,darkrasid/gitlabhq,jirutka/gitlabhq,htve/GitlabForChinese,mmkassem/gitlabhq,htve/GitlabForChinese,LUMC/gitlabhq,stoplightio/gitlabhq,iiet/iiet-git,jirutka/gitlabhq,t-zuehlsdorff/gitlabhq,dplarson/gitlabhq,t-zuehlsdorff/gitlabhq,mmkassem/gitlabhq,iiet/iiet-git,dreampet/gitlab,dplarson/gitlabhq,dreampet/gitlab,LUMC/gitlabhq