fix gunicorn arguments so that docker-registry can start without error
Fix bugs when using MySQL as index database

1. MySQLdb will raise ProgrammingError when table doesn't exists. Use engine.has_table to check whether table exists for compatible
2. VARCHAR requires a length on dialect mysql. String length limit is according to [Docker Hub's limit](https://registry.hub.docker.com/account/repositories/add/) and [docker's valid namespace and repo regex](https://github.com/docker/docker/blob/master/registry/registry.go#L214)
Ignore pedentic hacking warning

- H803 disables verifying that commit message doesn't end with a dot

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)
Fix hacking complaints

intermittently complaining travis about CORS not being a module

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)
Merge pull request #555 from irachex/mysql

Fix bugs when using MySQL as index database
Fixed get_tags whe using storage_path
Added test
Merge pull request #548 from visualphoenix/bugfix/gunicorn_wont_start

BUGFIX: modify run.py gunicorn arguments so docker-registry can start without error
blacklist backports.lzma v0.0.4

backports.lzma recently bumped up to v0.0.4, adding namespace support
to the package. However, they forgot to call declare_namespace() in
their __init__.py. This causes pip install failures when running

    pip install file:///docker-registry#egg=docker-registry

From inside the Dockerfile.
Merge pull request #573 from deis/hotfix-pin-lzma

blacklist backports.lzma v0.0.4
Bumped stable version
Merge pull request #553 from docker/486-get-tags

Fixed get_tags whe using storage_path
Better config exception handling

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)
Slight grammar thing

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)
Fix #521

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)
Fix test

Fixed broken path resolution

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)
Enhance tag error output

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)
Cleaner bugsnag abstraction

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)
Enhanced debugging infos

- removed version / config leakage in headers for all requests
- moved versions output to ping
- added more hosts debugging infos in the ping endpoint
- renamed _versions to _debug
- removed version from the / endpoint
- made / text configurable (issue)

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)
Remove unused status endpoint

Docker-DCO-1.1-Signed-off-by: Olivier Gambier <olivier@docker.com> (github: dmp42)