tests/vm: bump timeout for shutdown

On my fairly beefy machine the timeout was triggering leaving a
corrupted disk image due to power being pulled before the disk had
synced. Triple the timeout to avoid this.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20250304222439.2035603-13-alex.bennee@linaro.org>

tests/vm/basevm.py

@@ -83,7 +83,7 @@ class BaseVM(object):
     # command to halt the guest, can be overridden by subclasses
     poweroff = "poweroff"
     # Time to wait for shutdown to finish.
-    shutdown_timeout_default = 30
+    shutdown_timeout_default = 90
     # enable IPv6 networking
     ipv6 = True
     # This is the timeout on the wait for console bytes.