Fix tempest plugin cookicutter repo path

cookicutter expect ether git+<repo-url> or it has the
'git' in url, otherwise it give error
- http://paste.openstack.org/show/795952/

plugin cookicutter README is fine but tempest doc does
not mention about it and end up having error
- https://opendev.org/openstack/tempest-plugin-cookiecutter

Change-Id: Ifb12011ac901be57d49a6ae623a24a916837c07d
1 file changed