Fix createSession().

1. Loop condition was inverted. Creation process must not select key which exists on Redis.
2. Call generateSessionId() again, if sessionId already exists and not specified to be created.
3. According to org.apache.catalina.session.ManagerBase, createSession(id) return null if id specified and cannot create.
Add JedisPoolConfig settings.

- maxIdle
- minIdle
- maxActive
- maxWait