[Discovery] Fault detection should also check  cause exceptions for disconnects

The change introduced in #6686 checks for ConnectionTransportException during pinging. However, transport layer wraps it in  SendRequestTransportException
[TEST] Split up random bulks more often and also if the document set is smallish
[TEST] disable BWC tests for version < 1.1.0
[TEST] only call TestCluster#afterTest() if cluster was successfully initialized
[Discovery] immediately start Master|Node fault detection pinging

After a node joins the clusters, it starts pinging the master to verify it's health. Before, the cluster join request was processed async and we had to give some time to complete. With  #6480 we changed this to wait for the join process to complete on the master. We can therefore start pinging immediately for fast detection of failures. Similar change can be made to the Node fault detection from the master side.

Closes #6706
[TEST] Include mapping in failure
Docs: fixed ICU plugin documentation

add ICU Normalization CharFilter to docs

Closes #6711
[DOCS] Add information regarding _type parameter requirement for _mget

Closes #6670.
[DOCS] Add information regarding _type parameter requirement for _mget

Change ID to `[[mget-type]]`

Closes #6670.