Add a test for Ci::Pipeline#cancel_running:
Add a test for Ci::Pipeline#cancel_running:

Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7508#note_18622559

I didn't write an exhaustive one because we already have it on
HasStatus, from:

https://gitlab.com/gitlab-org/gitlab-ce/commit/b6a7a4783435a7fa34f26dbf3b16ab8e7ed21b88

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