run_tool_shed.sh error

Hello,

I have Galaxy (release_19.05) installed and running well on Debian 10 (Buster) with Python2.7. However, when I try to run `sh run_tool_shed.sh` to have a local Tool Shed, at some point I got the error below.

For information, I got the exactly same behaviour with Python3 (Galaxy runs well and got the same error when I try to start local Tool Shed).

Thank you for your help,
Joan

```
galaxy.datatypes.registry DEBUG 2019-09-10 16:34:33,772 [p:962,w:0,m:0] [MainThread] No build sites source located.
Traceback (most recent call last):
File "lib/galaxy/webapps/tool_shed/buildapp.py", line 69, in app_factory
app = UniverseApplication(global_conf=global_conf, **kwargs)
File "lib/galaxy/webapps/tool_shed/app.py", line 47, in __init__
from galaxy.webapps.tool_shed.model.migrate.check import create_or_verify_database
File "lib/galaxy/webapps/tool_shed/model/migrate/check.py", line 13, in
migrate_repository = repository.Repository(migrate_repository_directory)
File "/galaxy/.venv/local/lib/python2.7/site-packages/migrate/versioning/repository.py", line 77, in __init__
self.verify(path)
File "/galaxy/.venv/local/lib/python2.7/site-packages/migrate/versioning/repository.py", line 98, in verify
raise exceptions.InvalidRepositoryError(path)
InvalidRepositoryError: libwebapps/tool_shed/model/migrate
```

Start by reading run_tool_shed.sh, lib/galaxy/webapps/tool_shed/buildapp.py, and lib/galaxy/webapps/tool_shed/model/migrate/check.py, then trace the migration repository path reported in the traceback. Done means the local Tool Shed starts without InvalidRepositoryError.

Written by the indexing model from the issue text.