doc: fix testpmd playbook arguments for EC2

The docs incorrectly tell the user to set the override to true when it
needs to be false for EC2/PF based deployments.

Fixes: 359ff197 ("doc: provide the correct arguments for testpmd")
Signed-off-by: Nathan Brown <nathan.brown@arm.com>
Reviewed-by: Aditya Ambadipudi <aditya.ambadipudi@arm.com>

Change-Id: I194e2334ff6f741ed8ccf88cbedfecd14c06efd7