Multibucket setup QoL

[jvillafanez]

We might need several commands for the multibucket setup in order to make the life easier for the admin:

• Based on all the users available for ownCloud, we need a command to check if the target buckets are available
  • Show what users doesn't have its buckets available (with the target bucket)
  • Include an option to check for additional (required?) options in the bucket, such as CORS (which seems to be a problem with the current s3:list command)
  • Include option to create the target bucket if needed.
• Create all possible buckets, in case new users are added later
  • Include option to create the buckets with custom options and / or specific set of options (versioning, CORS, etc)
• Knowing a specific user, check the expected bucket for him. This way should be easier to check things for specific users in case we have to deal with more than 10k users.

Note that this should also help with testing: creating all the possible buckets will take a while in spite of having a local connection (36^3 ~= 46600 buckets) when you only need up to 5 for testing.
In addition, you don't know the buckets before creating the user and make ownCloud crash trying to access to a missing bucket (you might take note for the next time in order to create specific buckets for that set of users, if you don't lose that note).

@pmaier1 @PVince81 @micbar to put it somewhere in the backlog.