Mark some multistreams tests as xfail

These tests use curl output to assess if the behavior is
right or not.
However, the curl output can not be reliable in the current
situation where we look for a multiplexed connection, but
curl might have decided to reuse the connection if it is
available.

tests.yaml

@@ -1041,28 +1041,36 @@ tests:
       stderr: ''
       partstdout: 'NOERR'
 
+      # This test might fail
+      # this is due to the fact that it will check that libcurl
+      # uses HTTP/2 streams or sometimes the connection is
+      # available very quickly making unnecessary to use
+      # different streams
     - exe : './homer.py'
-      name: '[doh] Multistreams with 2 requests'
+      name: '[doh] Multistreams with 3 requests (can fail)'
       markers:
           - 'doh'
           - 'streams'
+          - 'xfail'
       args:
           - '-v'
           - '--multistreams'
           - '--file'
           - 'input_file'
           - '--repeat'
-          - '2'
-          - 'https://doh.bortzmeyer.fr'
+          - '3'
+          - 'https://doh.powerdns.org'
       retcode: 0
       partstderr: 'Multiplexed connection found'
       partstdout: 'Return code 200'
 
+      # same as previous test
     - exe : './homer.py'
       name: '[doh] Multistreams with 5 requests'
       markers:
           - 'doh'
           - 'streams'
+          - 'xfail'
       args:
           - '-v'
           - '--multistreams'