Ensure only one setup/teardown is allowed per scope

[norm]

Two parts to this:

• nested
• peer

[dstandish]

this one appears covered by test test_setup_block_nested @jedcunningham

[jedcunningham]

I blocked nested setups, but I didn't block 2 peer setups yet :)

[dstandish]

ok nice, i updated description

[jedcunningham]

You can now have more than 1 per scope, nothing remaining to do here.