'control_system' permission does not imply permission to provision

We need an extra permission checking method to cover provisioning (that
is, the 'configure_netboot' command) particularly, rather than just
checking that power commands can be executed.

This basically matches the historical (pre-19) behaviour where "direct"
provisioning was only offered if you had reserved the system.

Bug: 1144196
Change-Id: I85c708be56b7d2188ef27527c3f3188ba1bb602b