DATAREDIS-327 - Improve exception handling for all supported clients.

We now consistently return null in implementations of RedisConnectionFactory#translateExceptionIfPossible(RuntimeException ex)
in cases where we cannot translate the given exception into a more meaningful one complying with the spec of PersistenceExceptionTranslator. Introduced the ExceptionTranslationStrategy abstraction which allows to customise the translation of exceptions through the implementations PassThroughExceptionTranslationStrategy which returns null iif the Exception could not be translated and FallbackExceptionTranslationStrategy which returns a RedisSystemException wrapping the original Exception if it couldn't be translated properly.

This fix also solves the issues DATAREDIS-295, DATAREDIS-325, DATAREDIS-326.

Original pull request: #90.
DATAREDIS-333 - Use binary version of Jedis.evalsha()

* JedisConnection.eval() uses binary version of Jedis.eval()
* but JedisConnection.evalsha() uses string version of Jedis.evalsha()
* this commit changes JedisConnection.evalsha() to use binary version of Jedis.evalsha()

---

Original Pull Request: #91
CLA: 88220140729064528 (Jungtaek Lim)
DATAREDIS-324 - Add Redis Sentinel support.

We’ve added RedisSentinelConfiguration holding required information for connecting to redis sentinels. This can be used to set up ConnectionFeactory for HA environments.

**Using Jedis**
Providing RedisSentinelConfiguration will force the JedisConnectionFactory to use JedisSentinelPool for managing resources.

**Using Lettuce/JRedis/SRP**
There’s currently no support for sentinel in those clients.

**CI Build**
We’ve added makefile to build and set up redis instances for testing sentinel support on travis-ci. There’s already a section for redis cluster.
The cluster section is for whatever reason currently not working as the cluster nodes won’t start.
This will be fixed when we add redis-cluster support.

_side note:_ there’s an alternative fork of lettuce at mp911de/lettuce that already has sentinel support.
DATAREDIS-330 - Add support for Redis Sentinel commands.

Prepare issue branch.

squashme
DATAREDIS-330 - Add support for SENTINEL commands.

add support for commands:
  SENTINEL FAILOVER master
  SENTINEL SLAVES master
  SENTINEL REMOVE name
  SENTINEL MONITOR name ip port quorum