The setup in t7400-submodule-basic does a number of different
things to support different tests. Splitting it up makes the
test a little easier to read and should provide an opportunity
to move each piece of setup closer to the tests that require it.
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>