add a configurable for disabling the auto-generated isolated RSA key

some users won't want to utilize the RSA key we auto-generate for
isolated node SSH access, but will instead want to manage SSH
authentication by hand outside of Tower

see: https://github.com/ansible/ansible-tower/issues/7380

awx/settings/development.py

@@ -59,6 +59,7 @@ AWX_PROOT_ENABLED = True
 
 AWX_ISOLATED_USERNAME = 'root'
 AWX_ISOLATED_CHECK_INTERVAL = 1
+AWX_ISOLATED_LAUNCH_TIMEOUT = 30
 
 # Disable Pendo on the UI for development/test.
 # Note: This setting may be overridden by database settings.