fix: handle nonexistent git hooks directory

Summary:
It is possible for a .git subdirectory of a repository to not contain
the default hooks/ directory (perhaps the user deleted it, for example).

In this situation, we should just gracefully recreate it, rather than
dying.

Test Plan: delete .git/hooks in test repository, verify ka-clone —repair fixes it.

Reviewers: ethan, csilvers

Reviewed By: csilvers

Subscribers: anastassia

Differential Revision: https://phabricator.khanacademy.org/D18826

bin/ka-clone

@@ -120,8 +120,11 @@ def install_commit_linter():
 def _install_git_hook(template_name, hook_name):
     """Install a template as an executable git hook."""
     src = os.path.join(TEMPLATES_DIR, template_name)
-    dst = os.path.join(os.getcwd(), ".git", "hooks", hook_name)
-    shutil.copy(src, dst)
+    hooks_dir = os.path.join(os.getcwd(), ".git", "hooks")
+    if not os.path.isdir(hooks_dir):
+        os.makedirs(hooks_dir)
+    dst = os.path.join(hooks_dir, hook_name)
+    shutil.copyfile(src, dst)
     os.chmod(dst, (os.stat(dst)).st_mode | 0111)  # ensure chmod +x