Update factory for members and specs about members

We have added a sequence for login_name which is similar to the one for
emails in which the member name is incremented each time a new member is
saved.

In addition, we have updated all specs which asked for an explicit
login_name of member1 to use a regex looking only for member and some
digit.
Add test to ensure uniqueness of login_name
Merge pull request #2 from jcaudle/unique_usernames

Unique usernames