config cache prevents updating a value before expiration
Motivation
----------
```python
config.set('throttler', 'release_strategy', 'fifo')
config.set('throttler', 'release_strategy', 'grouped_fifo')
```
will result in a database duplicate exception because `config.set()` checks if there is already a value which will be `False` if you try to set a new value under the expiration time because it got set to `False` with the first command.


Modification
------------
change the `has_option()` check in `config.set()` to `has_option(use_cache=False)`


diff --git a/lib/rucio/core/config.py b/lib/rucio/core/config.py
index 7904e6459..a61f32079 100644
--- a/lib/rucio/core/config.py
+++ b/lib/rucio/core/config.py
@@ -200,7 +200,7 @@ def set(section, option, value, session=None):
     :param session: The database session in use.
     """
 
-    if not has_option(section=section, option=option, session=session):
+    if not has_option(section=section, option=option, use_cache=False, session=session):
         new_option = models.Config(section=section, opt=option, value=value)
         new_option.save(session=session)
     else:
['lib/rucio/core/config.py']