Fixing db authentication error- update database.py

Related to this issue:
https://groups.google.com/forum/#!topic/atomate/Q0ege6lPdqs

I had the same error. When I passed the database name into authsource it seemed to fix this issue.

Author: mhsiron

atomate/utils/database.py

@@ -128,6 +128,8 @@ def from_db_file(cls, db_file, admin=True):
         kwargs = {}
         if "authsource" in creds:
             kwargs["authsource"] = creds["authsource"]
+        else:
+            kwargs["authsource"] = creds["database"]
 
         return cls(creds["host"], int(creds["port"]), creds["database"], creds["collection"],
                    user, password, **kwargs)