Add user type in ListUsers API

[bigdatasourav]

Need to fetch the user type - Self, Owner

[rajlearner17]

Hi team, just checking if there will be any help with this issue to support user type.

bluemix-go/api/usermanagement/usermanagementv2/user_invite.go

Line 60 in 56edc36

//ListUsers returns all the users in the account