Make frozenage less reliant on changing _frozenlinks

The mtime of a file in OBS is the time this content was created for the
first time. As such if the target project isn't moving for a week,
staging select will keep asking you to freeze - even if you just froze.

So instead of relying on OBS to tell the true mtime, set an attribute
in the staging project and read from it. This also gives a way to check
in the webui for the last freeze time

Fixes #2462

dist/obs/OSRT:FreezeTime.xml

@@ -0,0 +1,5 @@
+<definition name="FreezeTime" namespace="OSRT">
+  <description>Date and time of the last call of freeze (updating _frozenlinks)</description>
+  <count>1</count>
+  <modifiable_by role="maintainer"/>
+</definition>

osclib/freeze_command.py

@@ -1,7 +1,9 @@
 import time
+from datetime import datetime, timezone
 from urllib.error import HTTPError
 from lxml import etree as ET
 import osc.core
+from osclib.core import attribute_value_save
 
 MAX_FROZEN_AGE = 6.5
 
@@ -197,6 +199,7 @@ class FreezeCommand(object):
 
         url = self.api.makeurl(['source', self.prj, '_project', '_frozenlinks'], {'meta': '1'})
         self.api.retried_PUT(url, ET.tostring(flink))
+        attribute_value_save(self.api.apiurl, self.prj, 'FreezeTime', datetime.now(timezone.utc).isoformat())
 
     def receive_sources(self, prj, sources, flink):
         url = self.api.makeurl(['source', prj], {'view': 'info', 'nofilename': '1'})

osclib/stagingapi.py

@@ -879,6 +879,12 @@ class StagingAPI(object):
         :param project: project to check
         :return age in days(float) of the last update
         """
+        freezetime = attribute_value_load(self.apiurl, project, 'FreezeTime')
+        if freezetime:
+            freezetime = datetime.fromisoformat(freezetime)
+            tz_info = freezetime.tzinfo
+            return (datetime.now(tz_info) - freezetime).total_seconds() / 3600 / 24
+        # fallback: old method
         root = ET.fromstring(self._fetch_project_meta(project))
         for entry in root.findall('entry'):
             if entry.get('name') == '_frozenlinks':