phd xtask could be more helpful if propolis-server does not compile

I'm not sure why this is happening, but I wanted to file an issue for a QOL improvement with PHD.

I tried to run the PHD tests with pfexec cargo xtask run phd

That hung for awhile like this:

jordan@atrium ~/propolis $ pfexec cargo xtask phd run
   Compiling propolis-server

After some time I CTRL+C'd it and it turns out propolis-server didn't compile on the branch I was working on. The xtask output could be more helpful here.

I tried running the xtask a second time, and it did eventually tell me something was worng:

Error: Failed to build propolis-server

Caused by:
    Cargo command failed: The cargo subcommand returned an error.
       Compiling illumos-utils v0.1.0 (https://github.com/oxidecomputer/omicron?rev=becbbb616f5f18b59cc42e511c148734c2ba3831#becbbb61)
       Compiling oximeter-schema v0.1.0 (https://github.com/oxidecomputer/omicron?branch=main#b8efb9a0)
       Compiling sled-hardware-types v0.1.0 (https://github.com/oxidecomputer/omicron?branch=main#b8efb9a0)
       Compiling oxql-types v0.1.0 (https://github.com/oxidecomputer/omicron?branch=main#b8efb9a0)
       Compiling gateway-client v0.1.0 (https://github.com/oxidecomputer/omicron?branch=main#b8efb9a0)
       Compiling internal-dns-resolver v0.1.0 (https://github.com/oxidecomputer/omicron?branch=main#b8efb9a0)
       Compiling nexus-sled-agent-shared v0.1.0 (https://github.com/oxidecomputer/omicron?branch=main#b8efb9a0)
       Compiling oximeter v0.1.0 (https://github.com/oxidecomputer/omicron?branch=main#b8efb9a0)
       Compiling oximeter-instruments v0.1.0 (https://github.com/oxidecomputer/omicron?branch=main#b8efb9a0)
       Compiling oximeter-db v0.1.0 (https://github.com/oxidecomputer/omicron?branch=main#b8efb9a0)
       Compiling sled-hardware-types v0.1.0 (https://github.com/oxidecomputer/omicron?rev=becbbb616f5f18b59cc42e511c148734c2ba3831#becbbb61)
       Compiling trust-quorum-types-versions v0.1.0 (https://github.com/oxidecomputer/omicron?rev=becbbb616f5f18b59cc42e511c148734c2ba3831#becbbb61)
       Compiling bootstore v0.1.0 (https://github.com/oxidecomputer/omicron?rev=becbbb616f5f18b59cc42e511c148734c2ba3831#becbbb61)
       Compiling nexus-types v0.1.0 (https://github.com/oxidecomputer/omicron?branch=main#b8efb9a0)
       Compiling trust-quorum-types v0.1.0 (https://github.com/oxidecomputer/omicron?rev=becbbb616f5f18b59cc42e511c148734c2ba3831#becbbb61)
       Compiling sled-agent-types-versions v0.1.0 (https://github.com/oxidecomputer/omicron?rev=becbbb616f5f18b59cc42e511c148734c2ba3831#becbbb61)
       Compiling sled-agent-types v0.1.0 (https://github.com/oxidecomputer/omicron?rev=becbbb616f5f18b59cc42e511c148734c2ba3831#becbbb61)
       Compiling sled-agent-client v0.1.0 (https://github.com/oxidecomputer/omicron?rev=becbbb616f5f18b59cc42e511c148734c2ba3831#becbbb61)
       Compiling nexus-client v0.1.0 (https://github.com/oxidecomputer/omicron?branch=main#b8efb9a0)
       Compiling dice-verifier v0.3.0-pre0 (https://github.com/oxidecomputer/dice-util?rev=1d3084b514389847e8e0f5d966d2be4f18d02d32#1d3084b5)
       Compiling vm-attest v0.1.0 (https://github.com/oxidecomputer/vm-attest?rev=2cdd17580a4fc6c871d24797016af8dbaac9421d#2cdd1758)
       Compiling oximeter-producer v0.1.0 (https://github.com/oxidecomputer/omicron?branch=main#b8efb9a0)
       Compiling crucible v0.0.1 (https://github.com/oxidecomputer/crucible?rev=a945a32ba9e1f2098ce3a8963765f1894f37110b#a945a32b)
       Compiling propolis v0.1.0 (/home/jordan/propolis/lib/propolis)
       Compiling propolis-server v0.1.0 (/home/jordan/propolis/bin/propolis-server)
    error: could not compile `propolis-server` (lib) due to 2 previous errors
    warning: build failed, waiting for other jobs to finish...
    

Start with the cargo xtask run phd entry point and reproduce the delayed propolis-server compilation failure. Check how the build error is reported, then make the PHD command provide clearer progress or failure output; done means a failed build is identified promptly instead of appearing hung.