Update zen.asciidoc

Tidied up the "No master block" asciidoc
Update cluster.asciidoc

Fixed asciidoc on cluster module page
Update cluster.asciidoc - fix invalid asciidoc
[TEST] assign a name to the transport client created within ExternalTestCluster

The transport client created within ExternalTestCluster needs a name that follows our naming convention otherwise the thread leak filter barfs when running tests against an external cluster. Used "transport_client_external_{n}" where n gets incremented every time a new external cluster gets created. Updated thread leak filters rules to ignore threads created by such transport client.
Test: make field `id` is defined in mapping, so sort can't fail
Docs: Updated JVM version
release [1.4.0]
Bump to 1.4.1-SNAPSHOT

Adds Version constant and updates the :version: key in index.asciidoc
1.4.1 is a SNAPSHOT release, pass `true` for Version constructor
Clarified support of index aliases

Clarified the support of index aliases in the snapshot section for the `indices` parameter.
Update Sonatype release link in build_release.py
[TEST] fixed scriptedMetricTests

The tests were failing because there was a shard which didn't get any documents and the tests assumed all shards had documents. This commit fixes this assumption
[docs] fix typo in getting-started

Closes #8354
[TRANSLOG] Translog leaks filehandles if it's corrupted or truncated

If the translog file is corrupted or truncated the stream is never closed
and the filehandle leaks. This commit closes the stream in the case of an
exception.
Indices API: Fixed backward compatibility issue

If a 1.4 node needs to forward a GET index API call to a <1.4 master it cannot use the GET index API endpoints as the master has no knowledge of it. This change detects that the master does not understand the initial request and instead tries it again using the old APIs. If these calls also do not work, an error is returned

Closes #8364
[TEST] BWC test might not start enough nodes for GREEN status
Internal: Don't pass acceptdocs down to parents filter.

Closes #8390.
[TEST] fix term_vector realtime test to call wait for green and use no replicas

If a shard (e.g. replica) gets initialized after we indexed the document it gets refreshed internally and we find the doc and its term_vectors, thus the test fails
Update multi-get.asciidoc

Documented that the fields parameter can be passed in the query string.

Closes #4006
Docs: Improve the exists/missing filters documentation

Closes #7274