Changed default redis_dir in order to be FHS compliant.

Hello,

Small fix: Make redis use /var/lib/redis for its home dir by default. As of now, this role uses a non-standard dir, since an application should not have a dir for it directly on the root of /var/. More info at http://refspecs.linuxfoundation.org/FHS_2.3/fhs-2.3.html#VARLIBVARIABLESTATEINFORMATION

Thank you!

PS: Could you upgrade the role in Ansible Galaxy? Thank you very much!
PPS: I've also fixed redis_sentinel_dir in the same fashion.