Discover the correct default config dir

Change the tempest init to discover the correct default config
dir. When no config dir is specified, we should use a sane default.
Which is /etc/tempest when tempest is installed system-wide, or
[virtualenv_root]/etc/tempest when tempest is installed in a
virtualenv.

Closes bug #1480389

Change-Id: I88aee53dbbe9262fbb4bf1686b18e1371f00bf69
1 file changed