[IMPR] format db_hostname the same as db_name

The current Wiki Replicas setup allows querrying any db replica from any
host since all of the wikis are one all of the hosts.
With the 2020 redesign each host will only have some wikis, so format
the hostname with the database name.

db_hostname is replaced by db_hostname_format.

Change-Id: Ife681250a279577b79ad80f7a9aa42b069ad4bb6

pywikibot/config2.py

@@ -113,6 +113,7 @@ class _ConfigurationDeprecationWarning(UserWarning):
     'available_ssl_project', 'fake_user_agent', 'interwiki_contents_on_disk',
     'line_separator', 'LS', 'panoramio', 'proxy', 'special_page_limit',
     'sysopnames', 'use_mwparserfromhell', 'use_SSL_onlogin', 'use_SSL_always',
+    'db_hostname',
 }
 _future_variables = {'absolute_import', 'division', 'unicode_literals'}
 
@@ -689,10 +690,10 @@ def register_families_folder(folder_path):
 # db_name_format can be used to manipulate the dbName of site.
 #
 # Example for a pywikibot running on wmflabs:
-# db_hostname = 'enwiki.analytics.db.svc.eqiad.wmflabs'
+# db_hostname_format = '{0}.analytics.db.svc.eqiad.wmflabs'
 # db_name_format = '{0}_p'
 # db_connect_file = user_home_path('replica.my.cnf')
-db_hostname = 'localhost'
+db_hostname_format = 'localhost'
 db_username = ''
 db_password = ''
 db_name_format = '{0}'

pywikibot/data/mysql.py

@@ -56,7 +56,7 @@ def mysql_query(query: str, params=None,
     else:
         credentials = {'read_default_file': config.db_connect_file}
 
-    with closing(pymysql.connect(config.db_hostname,
+    with closing(pymysql.connect(config.db_hostname_format.format(dbname),
                                  db=config.db_name_format.format(dbname),
                                  port=config.db_port,
                                  charset='utf8',