Rename TestConnectionImplementation in hbase-it to fix javadoc failure

discussed during release of 2.5.3RC0 https://lists.apache.org/thread/b34lgz3yy8vkv4fbbxj4mvtjyjrp4m6p

I found a javadoc problem introduced by HBASE-27498 with the same test class shared the same package prefix such that the javadoc failed with a unclear java.lang.NullPointerException.

• hbase-it/src/test/java/org/apache/hadoop/hbase/client/TestConnectionImplementation.java
• hbase-server/src/test/java/org/apache/hadoop/hbase/client/TestConnectionImplementation.java

after renaming hbase-it/src/test/java/org/apache/hadoop/hbase/client/TestConnectionImplementation.java to hbase-it/src/test/java/org/apache/hadoop/hbase/client/TestConnectionImplementationCacheMasterState.java should fix this issue.