Rewrite remoteload_test integration tests (#4783)

* Better error message when git clone fails

* support file:// URLs

* rewrite remoteload_test

* lint and test fix

* fixes for kverey's comments

* document file:// remote load

* replace assert with require where appropriate

* add tests for file:// without git suffix

* fixes plus pr review from natasha

* fixes for review, lint

* revert changes to error handling

* fix skipped test

api/internal/git/gitrunner.go

@@ -46,9 +46,9 @@ func (r gitRunner) run(args ...string) error {
 		cmd.String(),
 		r.duration,
 		func() error {
-			_, err := cmd.CombinedOutput()
+			out, err := cmd.CombinedOutput()
 			if err != nil {
-				return errors.Wrapf(err, "git cmd = '%s'", cmd.String())
+				return errors.Wrapf(err, "failed to run '%s': %s", cmd.String(), string(out))
 			}
 			return err
 		})