obs: put git submodules into source packages

We started using git submodules with osmo-trx. Adjust the obs scripts
to actually make the git submodules part of the source packages.

Note that this didn't fail in jenkins before with the rpm build
verification, as jenkins updates git submodules on its own.

Fix for:
[  165s] Makefile.am:32: error: required directory ./osmocom-bb/src/host/trxcon does not exist

Change-Id: I51b423f3885d6ead5c21a83bdf8ef6051dc34fe3

scripts/obs/lib/git.py

@@ -56,6 +56,8 @@ def checkout(project, branch):
     lib.run_cmd(["git", "checkout", "-f", branch], cwd=repo_path)
     print(f"{project}: 'git reset --hard {branch}'")
     lib.run_cmd(["git", "reset", "--hard", branch], cwd=repo_path)
+    print(f"{project}: 'git submodule update --init'")
+    lib.run_cmd(["git", "submodule", "update", "--init"], cwd=repo_path)
 
 
 def checkout_from_review(project, gerrit_id):