tests: propagate errors from open_temp_repo() instead of exiting

This makes it slightly easier to debug test failures when one test
opens a repo, has a failure, and doesn't get a chance to close it for
the next test. Now, instead of getting no feedback, we at least see
test failure information.

tests/test_helpers.c

@@ -217,10 +217,9 @@ int copydir_recurs(const char *source_directory_path, const char *destination_di
 
 int open_temp_repo(git_repository **repo, const char *path)
 {
-	if (copydir_recurs(path, TEMP_REPO_FOLDER) < GIT_SUCCESS) {
-		printf("\nFailed to create temporary folder. Aborting test suite.\n");
-		exit(-1);
-	}
+	int error;
+	if ((error = copydir_recurs(path, TEMP_REPO_FOLDER)) < GIT_SUCCESS)
+		return error;
 
 	return git_repository_open(repo, TEMP_REPO_FOLDER);
 }