[TEST] Take compatibility version into account for XContentType
randomization

We randomize the XContentType to test deriving the content type on all
APIs. Yet, BWC tests run against versions where CBOR wasn't around
this commit ensures we don't use CBOR when compatibility version is
less than `1.2.0`

Closes #6691
[Discovery] Handle ConnectionTransportException during a Master/Node fault detection ping

Both the Master and Node fault detection register themselves to be notified when a node disconnects to be able to respond to it accordingly. As such, when a ConnectionTransportException was raised on a ping request, it was not handled as it is already handled somewhere else. However, this does introduce a racing condition, if the disconnect  happen during a period where there is no current master (minimum_master_node breach) at which time the fault detection is not active. In this case, we will only discover the disconnect error during the ping request, so we have to respond accordingly.

Closes #6686
[TEST] Don't wait for relocations - the ensureYellow() call does that already
[TEST] Also do waitForConcreteMappingsOnAll() call for the .percolator type.
Percolator: improve logging and cleanup try-catch statement for percolator query loading.
[TEST] use pre 1.2.0 MATCH_ALL version if we test BWC for pre 1.2.0
clean shard bulk mapping update to only use type
today we track both the index name and type for mapping updates in the shard bulk action, but we only work against on index in this level, so no need to track the index name itself
closes #6695