HDFS-15940. Fixing and refactoring tests specific to Block recovery. (#2902)

* HDFS-15940. Fixing and refactoring tests specific to Block recovery.(#2844). Contributed by Viraj Jasani
(cherry picked from commit 2b5fd34)

 Conflicts:
	hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestBlockRecovery.java

* HDFS-15940. Fix TestBlockRecovery2#testRaceBetweenReplicaRecoveryAndFinalizeBlock (ADDENDUM) (#2874)

(cherry picked from commit 56bd968)
(cherry picked from commit 4994b73)

Co-authored-by: Viraj Jasani <vjasani@apache.org>

Author: jojochuang