jenkins-helpers.sh: Create a more robust clone for git.linaro.org

new function git_clone_git_linaro_org()
It makes successive tries
 - https access on git.linaro.org
 - ssh access on git.linaro.org
 - gitlab mirrored gitlab.com repo

Change-Id: I9a17b3da6f50df97bcd83f028fb3263c57abfd86
1 file changed