Remove 100% coverage requirement

Older Elasticsearch versions will not support all of the features
of PyEQS (such as aggregations).  We do not want these tests to
run against old ES versions, so we skip them.  However, this means
that tests run against older ES versions will no longer maintain
100% test coverage.  For now, our only hope is to rely on ourselves
to maintain discipline and continue to keep 100% coverage against
the newest version of ES.