Try to get Member or member role

Try to get Member or member role

Keystone roles are case insensitive and Apex declares member which
couldn't be detected. Then conflict occured when creating the
mandatory role [1].

It now searches the default role in lower case too.

[1] https://build.opnfv.org/ci/view/functest/job/functest-apex-baremetal-daily-master/141/console

Change-Id: I687ecfe768ab4717fdb42a135c4bf9b76733ffd9
Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>
(cherry picked from commit 4f89564b20e9c3462614706a616d469540631786)