test(ballon): add wait_for_up in test_deflate_on_oom

test_deflate_on_oom started failing recently while
calling `make_guest_dirty_memory()` and instantiating
an SSH object. It is likely because the guest
is not able to set up the SSH server by the time
we try to connect for the first time.

Signed-off-by: Nikita Kalyazin <[email protected]>

Author: kalyazin

tests/integration_tests/functional/test_balloon.py

@@ -198,6 +198,7 @@ def test_deflate_on_oom(uvm_plain_any, deflate_on_oom):
 
     # Start the microvm.
     test_microvm.start()
+    test_microvm.wait_for_up()
     firecracker_pid = test_microvm.firecracker_pid
 
     # We get an initial reading of the RSS, then calculate the amount