Test package refactoring

The new tests layout works as follows:

- Test code for common APIs are defined in couchbase/tests/cases.

- Test code does not have a test prefix or suffix, instead, we use the
  _t suffix internally to denote that this is a test.

- Test entry points should use 'test'

- Test entry points should use the couchbase.tests.importer module to
  import the test code into their own namespace/modules. They must
  supply a suffix to identify the implementation for the test, as well
  as a configuration mixin class which directs the base class which
  implementation to use.

Change-Id: Iffffb8efeb6c8aa3fca53e46beb1fbc2fe755500
Declare Connection_lcb_version as being METH_NOARGS

Change-Id: I408efab697eee9cf327e0e70e5238508549038cc