temporarily increase the timeout to 15 mins

We need to increase the timeout for each test to 15 minutes because we
are experiencing timeouts when running the tests. I think this might be
actually related to the hosts running the CI, because some early
investigations by aghecen@amazon.com show that the threads are blocked
on doing epoll_wait. This is odly similar to the issue discussed here
related to epoll: https://lore.kernel.org/all/Y1pY2n6E1Xa58MXv@kroah.com/

For more details, check: https://github.com/rust-vmm/community/issues/137

Signed-off-by: Andreea Florescu <fandree@amazon.com>

.buildkite/autogenerate_pipeline.py

@@ -111,7 +111,7 @@ class BuildkiteStep:
                     }
                 }
             ],
-            'timeout_in_minutes': 5
+            'timeout_in_minutes': 15
         }
 
     def _set_platform(self, platform):