Make configuring client nodes stricter with less inference

[sethmlarson]

Currently all of the following methods for configuring clients work in 7.x:

Elasticsearch() # [{}]
Elasticsearch([{}]) # [{}]
Elasticsearch("localhost") # [{'host': 'localhost'}]
Elasticsearch("localhost:9443") # [{'host': 'localhost', 'port': 9443}]
Elasticsearch("http://localhost") # [{'host': 'localhost'}]
Elasticsearch("http://localhost:9443") # [{'host': 'localhost', 'port': 9443}]
Elasticsearch("http://user:pass@localhost") # [{'host': 'localhost', 'http_auth': 'user:pass'}]
Elasticsearch("http://user:pass@localhost:9443") # [{'host': 'localhost', 'port': 9443, 'http_auth': 'user:pass'}]
Elasticsearch("http://localhost/a") # [{'host': 'localhost', 'url_prefix': '/a'}]
Elasticsearch("http://localhost:9443/a") # [{'host': 'localhost', 'port': 9443, 'url_prefix': '/a'}]
Elasticsearch("https://localhost") # [{'host': 'localhost', 'port': 443, 'use_ssl': True}]
Elasticsearch("https://localhost:9443") # [{'host': 'localhost', 'port': 9443, 'use_ssl': True}]

Any configuration that doesn't mention host, port, or use_ssl uses the default values of localhost, 9200, and False which can be super confusing in some situations! Proposed change is to make it impossible to configure a client with inference unless using the default client Elasticsearch().

So the following configurations would be disallowed:

Elasticsearch("localhost") # [{'host': 'localhost'}]
Elasticsearch("localhost:9443") # [{'host': 'localhost', 'port': 9443}]
Elasticsearch("http://localhost") # [{'host': 'localhost'}]
Elasticsearch("http://localhost:9443") # [{'host': 'localhost', 'port': 9443}]
Elasticsearch("http://user:pass@localhost") # [{'host': 'localhost', 'http_auth': 'user:pass'}]
Elasticsearch("http://localhost/a") # [{'host': 'localhost', 'url_prefix': '/a'}]
Elasticsearch("https://localhost") # [{'host': 'localhost', 'port': 443, 'use_ssl': True}]

and the following will be allowed:

Elasticsearch() # [{}]
Elasticsearch([{}]) # [{}]
Elasticsearch("http://localhost:9443") # [{'host': 'localhost', 'port': 9443}]
Elasticsearch("http://user:pass@localhost:9443") # [{'host': 'localhost', 'port': 9443, 'http_auth': 'user:pass'}]
Elasticsearch("http://localhost:9443/a") # [{'host': 'localhost', 'port': 9443, 'url_prefix': '/a'}]
Elasticsearch("https://localhost:9443") # [{'host': 'localhost', 'port': 9443, 'use_ssl': True}]

[sethmlarson]

This is resolved in #1753