Move testsuite/tests to src/plivo/tests

This is to simplify test discovery and avoid mucking about with sys.path
Rename src/examples/freeswitch/outbound/*test.py to *example.py

They were being included in test discovery and were not really tests.
Include example of running tests in README.

When I tried to run the test with the old files, I had to read the
code and do a lot of discovering by myself.
Merge pull request #4 from darylyu/move_tests

Move tests