Voting config exclusions API: node_name is not parsed as a comma-separated list

[barkbay]

Elasticsearch version (bin/elasticsearch --version): >=7

Description of the problem including expected versus actual behavior: In the voting config exclusions API the node_name parameter is converted into an array of 1 element and not processed as a comma-separated list of individual filters as expected.

See line 52 here:

elasticsearch/server/src/main/java/org/elasticsearch/rest/action/admin/cluster/RestAddVotingConfigExclusionAction.java

Lines 50 to 54 in 1038f23

	String nodeName = request.param("node_name");
	AddVotingConfigExclusionsRequest votingConfigExclusionsRequest = new AddVotingConfigExclusionsRequest(
	new String[]{nodeName},
	TimeValue.parseTimeValue(request.param("timeout"), DEFAULT_TIMEOUT, getClass().getSimpleName() + ".timeout")
	);

Steps to reproduce:

1. setup a 3 master nodes cluster
2. Try to add at least 2 master nodes to the voting exclusions list, e.g. do a POST on http://es:9200/_cluster/voting_config_exclusions/node-1,node-2

Provide logs (if relevant):

400 Bad Request: add voting config exclusions request for [node-1,node-2] matched no master-eligible nodes"

[elasticmachine]

Pinging @elastic/es-distributed