Add --clean option to tools metadata generation
Fix whitespace
Merge pull request #1068 from wallyworld/generate-metadata-delete-option

Add --clean option to tools metadata generation

Fixes: https://bugs.launchpad.net/bugs/1390250

Add a --clean option to "juju metadata generate-tools"

This will delete any exiting metadata for the specified stream, so that new metadata replaces instead of merging. Metadata for other streams is untouched.