This PR introduces two new commands:
1. `list-users` which lists all users in boltdb
2. `add-superadmin` which can be user to promote existing users to
superadmins, or creates new users that are superadmins
Currently this work was done as a separate binary, but the intention is
to make it a part of the `chronograf` binary.
Connect https://github.com/influxdata/chronograf/issues/2744
ischolten
Michael Desa
Luke Morris