Read output before waiting for process to end

Sometimes a subprocess will not exit until it was able to write its
output to stdout/stderr. By waiting _after_ we read the subprocess
output, we avoid this potential bug.
Call popen with an array instead of a string
Bypass the shell in SeedHelper
 Merge branch 'shell_style' into 'master'

Use the new shell command style
Merge branch 'master' of github.com:gitlabhq/gitlab_git