Make ROOTDIR determination more robust

Remove unused CLIENTDIR and replace it with a TESTDIR
(pointing to rootdir/keystoneclient/tests) and use
normpath for determining the full path of rootdir.

This change is needed if keystoneclient/ is a symlink
and etc/ is in a different directory hierarchy.

Change-Id: Ice9165ef25ec0200ccfb50c2f2f3121a136652a2
Merge "Make ROOTDIR determination more robust"