`omicron-dev run-all` depends on libipcc?!

[iximeow]

I've noticed this before but @lgfa29 mentioning it is what nudged me to actually figure out why I'd seen it: omicron-dev depends on gateway-test-utils to get gateway_test_utils::setup::DEFAULT_SP_SIM_CONFIG, but that also has gateway-test-utils -> omicron-gateway -> illumos-utils -> ipcc -> libipcc. and at that point, if you're on an illumos system but not Helios (such as an OmniOS), we'll try linking against non non-existent libipcc and die with = note: ld: fatal: library -lipcc: not found.

in the past I'd worked around this by patching the libipcc dependency locally to use the mocks even on illumos, but it's an awkward patch to carry and seems pretty solvable with a bit of motion here.

edit: there's a second (more direct) path to ipcc too, which is through nexus-test-utils. that directly depends on omicron-sled-agent.