Clean Redis keys before testing

https://build.spring.io/browse/INT-FATS5IC-400

When we run several concurrent builds (e.g. CI) and use the same shared
Redis server we may end up with the case when one process reads data
populated by another because we use the same key (groupId in our case)

* Fix `RedisMessageGroupStoreTests` to use `UUID.randomUUID()`
for the `groupId`

**Cherry-pick to 4.3.x**

# Conflicts:
#	spring-integration-redis/src/test/java/org/springframework/integration/redis/store/RedisMessageGroupStoreTests.java

Author: artembilan