dufs,restic-rest-server: fix certificate renewal tests

The configuration of caucase used here is to have certificates valid for
3*31 days and renew them 31 days before the expiration date.
This test was running the updater 2 months later, which by chance was
62 days at the time of the test was written, because this test was
written in July (both July and August have 31 days), but this does not
work in other months.
Adjust the test to run the updater using a fixed number of days in the
future.

software/dufs/test/test.py

@@ -131,14 +131,14 @@ class TestFileServer(SlapOSInstanceTestCase):
           return cnx.sock._sslobj.getpeercert()
 
     cert_before = _getpeercert()
-    # execute certificate updater two month later, when it's time to renew certificate.
+    # execute certificate updater when it's time to renew certificate.
     # use a timeout, because this service runs forever
     subprocess.run(
       (
         'timeout',
         '5',
         'faketime',
-        '+2 months',
+        '+63 days',
         os.path.join(
           self.computer_partition_root_path,
           'etc/service/dufs-certificate-updater'),

software/restic-rest-server/test/test.py

@@ -158,14 +158,14 @@ class TestResticRestServer(SlapOSInstanceTestCase):
           return cnx.sock._sslobj.getpeercert()
 
     cert_before = _getpeercert()
-    # execute certificate updater two month later, when it's time to renew certificate.
+    # execute certificate updater when it's time to renew certificate.
     # use a timeout, because this service runs forever
     subprocess.run(
       (
         'timeout',
         '5',
         'faketime',
-        '+2 months',
+        '+63 days',
         os.path.join(
           self.computer_partition_root_path,
           'etc/service/rest-server-certificate-updater'),