Do not return Jedis conns to pool after NPE

DATAREDIS-153

- Return conn to pool as broken resource if NPE
occurs (for example if a null key or value is given),
preventing later flush of OutputStream with incomplete
data

- Workaround Jedis issue in pub/sub tests that prevents
subscribing with a pooled connection

- Continue not using pool in conn tests, as they
are too brittle with potentially unclosed pipelines,
unexecuted txs, etc
Revert "Temp revert "Lazily instantiate shared Lettuce connection""

This reverts commit c6a2a4f7daf3aa00638fdc21bcb62542a11357b8.