validate number of indirect desc in pop_avail - #1188

control: job assigned to worker 01KZ4EPES7E3SF452Z94J3WH3B [factory aws, i-03945f70b22bb7d4f] (queued for 52 s)
...
task: starting task 0: "setup"
task: process exited: duration 4084 ms, exit code 0
...
task: starting task 1: "rust-toolchain"
task: process exited: duration 17144 ms, exit code 0
...
task: starting task 2: "authentication"
task: process exited: duration 16 ms, exit code 0
...
task: starting task 3: "clone repository"
task: process exited: duration 1381 ms, exit code 0
...
task: starting task 4: "build"
...
| + mv target/debug/propolis-server-debug.tar.gz /out/propolis-server-debug.tar.gz
| + mv target/debug/phd-runner.tar.gz /out/phd-runner.tar.gz
| + mv target/debug/propolis-tests-debug.tar.gz /out/propolis-tests-debug.tar.gz
| + cd /out
| + digest -a sha256 propolis-server-debug.tar.gz
| + digest -a sha256 phd-runner.tar.gz
task: process exited: duration 597214 ms, exit code 0
|W| found 6 output files
|W| uploading: /out/phd-run-with-args.sh (2573 bytes)
|W| uploaded: /out/phd-run-with-args.sh
|W| uploading: /out/phd-runner.sha256.txt (65 bytes)
|W| uploaded: /out/phd-runner.sha256.txt
|W| uploading: /out/phd-runner.tar.gz (192188229 bytes)
|W| uploaded: /out/phd-runner.tar.gz
|W| uploading: /out/propolis-server-debug.sha256.txt (65 bytes)
|W| uploaded: /out/propolis-server-debug.sha256.txt
|W| uploading: /out/propolis-server-debug.tar.gz (267706987 bytes)
|W| uploaded: /out/propolis-server-debug.tar.gz
|W| uploading: /out/propolis-tests-debug.tar.gz (224613145 bytes)
|W| uploaded: /out/propolis-tests-debug.tar.gz