Currently the "unique_last_password_count" attribute in keystone
configuration is set to "2", which enforces "cannot reuse the last
1 passwords" in history instead of "cannot reuse the last 2 passwords"
stated in security document.
This update changed "unique_last_password_count" attribute to "3" so
that keystone users password change rule complies with the document.
Closes-Bug: 1924772
Change-Id: I6a2de54336c7253022d49ecb118a315a7825c889
Signed-off-by: Andy Ning <andy.ning@windriver.com>
a4046414b6