There are several reasons for this. One is that the majority of
OpenStack packages behave this way. The second is that it makes writing
software that extends something easier to test (which is a clear usecase
for openstackclient) And third, tests/__init__.py implies a global
package named "tests" - which I'm pretty sure we're not providing.
Change-Id: Ic708ffd92aea78c2ffc1a8579af0587af4fca4ff