fix(test): eliminate sleep-based "wait for vm boot"

Microvms that have a network interface added to it will automatically
use ssh to wait for bootup, so use this to replace the 500ms sleep that
was not enough in some cases, leading to RuntimeError: ('Balloon config
error: Error creating the balloon device: Device not activated yet.',
{'fault_message': 'Balloon config error: Error creating the balloon
device: Device not activated yet.'}, <Response [400]>) errors on the
subsequent PATCH.

Signed-off-by: Patrick Roy <roypat@amazon.co.uk>

Author: roypat

tests/integration_tests/functional/test_api.py

@@ -8,7 +8,6 @@
 import platform
 import re
 import resource
-import time
 from pathlib import Path
 
 import packaging.version
@@ -1020,12 +1019,9 @@ def test_api_balloon(uvm_nano):
         )
 
     # Start the microvm.
+    test_microvm.add_net_iface()
     test_microvm.start()
 
-    # Give the balloon driver time to initialize.
-    # 500 ms is the maximum acceptable boot time.
-    time.sleep(0.5)
-
     # But updating should be OK.
     test_microvm.api.balloon.patch(amount_mib=4)