Add a juju subcommand for backup.
Add the backups create subcommand.
Clean up names and doc comments.
Adjust to changes in api/backups.
Add doc comments for some "public" fields.
Add more doc comments.
Remove superflous whitespace.
Add another doc comment.
Test --help in a less fragile way.
Trace an error.
Patch out the API client rather than the call to its method.
Add another doc comment.
Fix some outdated doc comments.
BackupsSuite -> BaseBackupsSuite.
Factor out patchAPIClient test helper.
Return fakeAPIClient from helpers.
Track args in fakeAPIClient.
Add a test for the notes arg for create.
Merge pull request #772 from ericsnowcurrently/backups-command

Add a juju subcommand for backup.

I've added a new juju subcommand "backups".  The command is itself a "supercommand", meaning it has its own subcommands.  This patch adds a single subcommand "create" (i.e. "juju backups create") which causes a new state backup to get created and stored, and prints the new backup ID.

This command is not yet a replacement for the "juju backup" command (which is implemented as a plugin).  That cannot happen until we add a "juju backups download" command, or at least a --download option to "juju backups create".