Fix permissions for tempest.conf

The current script uses 'sudo' to copy tempest.conf.sample and thus
the .conf file gets owned by root.  It then makes the permissions 644,
meaning that when the 'stack' user does the iniset() calls, it doesn't
have permisson on the .conf file.

Since the dir has been chowned to the stack user, it seems safe to
just copy the sample file in without sudo.  In addition, I moved the
$TEMPEST_CONFIG_DIR creation closer to the copy to make it clearer
what's going on.

Seems to be related to dc4dc7f03335e26ea3d86b6184f0475cc5f3d51b

Fixes bug: #1284378
Change-Id: I103b4e90cbcfa693c9cef319f4135868a1b83de3
Merge "Fix permissions for tempest.conf"
Merge branch 'master' of github.com:openstack-dev/devstack