automation: add default QEMU_TIMEOUT value if not already set

The expectation is that QEMU_TIMEOUT should be set as a Gitlab CI/CD
variable but if not we should be able to run the pipeline anyway.

Signed-off-by: Stefano Stabellini <stefano.stabellini@amd.com>
Reviewed-by: Michal Orzel <michal.orzel@amd.com>

automation/scripts/qemu-key.exp

@@ -1,6 +1,10 @@
 #!/usr/bin/expect -f
 
-set timeout $env(QEMU_TIMEOUT)
+if {[info exists env(QEMU_TIMEOUT)]} {
+    set timeout $env(QEMU_TIMEOUT)
+} else {
+    set timeout 1500
+}
 
 log_file -a $env(QEMU_LOG)