Change Gitlab::Popen to use arrays for commands
Make the Gitlab::Popen path argument optional
Make it possible to call Gitlab::Popen.popen
Adapt use of Gitlab::Popen to new style
Better redirect for edit blod from MergeRequest

If you cancel edit you will be redirected back to merge request
If you submit changes you will be redirected back to merge request

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
 Merge branch 'improve/edit_cancel' into 'master'

Better redirect for edit blobs from MergeRequest
 Merge branch 'gitlab_popen_array' into 'master'

Change Gitlab::Popen to only accept arrays as commands