add test case for submodule depth parameter
add test case for submodule depth parameter

Signed-off-by: Liam Beguin <ac8b122174024ef5e58ca7d6d989651e9bbfc948@gmail.com>

gitpython-developers/gitpython,gitpython-developers/GitPython,gitpython-developers/GitPython,gitpython-developers/gitpython