t7400: encapsulate setup code in test_expect_success

When running t7400 in a shell you observe more output than expected:

    ...
    ok 8 - setup - hide init subdirectory
    ok 9 - setup - repository to add submodules to
    ok 10 - submodule add
    [master (root-commit) d79ce16] one
     Author: A U Thor <author@example.com>
     1 file changed, 1 insertion(+)
     create mode 100644 one.t
    ok 11 - redirected submodule add does not show progress
    ok 12 - redirected submodule add --progress does show progress
    ok 13 - submodule add to .gitignored path fails
    ...

Fix the output by encapsulating the setup code in test_expect_success

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: stefanbeller

t/t7400-submodule-basic.sh

@@ -126,8 +126,10 @@ test_expect_success 'submodule add' '
 	test_cmp empty untracked
 '
 
-test_create_repo parent &&
-test_commit -C parent one
+test_expect_success 'setup parent and one repository' '
+	test_create_repo parent &&
+	test_commit -C parent one
+'
 
 test_expect_success 'redirected submodule add does not show progress' '
 	git -C addtest submodule add "file://$submodurl/parent" submod-redirected \