provision: Early-exit in template_database_status.

This is a pure refactor, and we just early-exit
in case the datbase doesn't exist (knowing that
that can be a bit of a lie now--see the comment
I added.)

zerver/lib/test_fixtures.py

@@ -224,7 +224,17 @@ def template_database_status(database_type: str) -> str:
     if not os.path.exists(status_dir):
         os.mkdir(status_dir)
 
-    if database_exists(database.database_name):
+    if not database_exists(database.database_name):
+        # TODO: It's possible that `database_exists` will
+        #       return `False` even though the database
+        #       exists, but we just have the wrong password,
+        #       probably due to changing the secrets file.
+        #
+        #       The only problem this causes is that we waste
+        #       some time rebuilding the whole database, but
+        #       it's better to err on that side, generally.
+        return 'needs_rebuild'
+
     # To ensure Python evaluates all the hash tests (and thus creates the
     # hash files about the current state), we evaluate them in a
     # list and then process the result
@@ -257,8 +267,6 @@ def template_database_status(database_type: str) -> str:
 
     return 'current'
 
-    return 'needs_rebuild'
-
 def destroy_leaked_test_databases(expiry_time: int = 60 * 60) -> int:
     """The logic in zerver/lib/test_runner.py tries to delete all the
     temporary test databases generated by test-backend threads, but it