fix: Check for required services running after frappe init

Each site on a single app server can run on separate DBMS' on separate
servers. This site specific config resides in each site's
site_config.json file. Thereby, we need to load site's config before
checking for service's availability.

frappe/migrate.py

@@ -159,13 +159,13 @@ class SiteMigration:
 		"""Run Migrate operation on site specified. This method initializes
 		and destroys connections to the site database.
 		"""
-		if not self.required_services_running():
-			raise SystemExit(1)
-
 		if site:
 			frappe.init(site=site)
 			frappe.connect()
 
+		if not self.required_services_running():
+			raise SystemExit(1)
+
 		self.setUp()
 		try:
 			self.pre_schema_updates()