Kernel configuration options still don't quite work as intended

[nwf]

The boring invocation of cheribuild.py run-riscv64-purecap --list-kernels works fine, but if I have --cheribsd-riscv64-purecap/kernel-config set (to CHERI-CAPREVOKE-QEMU, say) on the command line or in the config json, then --list-kernels explodes:

Traceback (most recent call last):
  File "/cheri/source/cornucopia-modernize/cheribuild/cheribuild.py", line 42, in <module>
    main()
  File "/cheri/source/mainline/cheribuild/pycheribuild/__main__.py", line 258, in main
    run_and_kill_children_on_exit(real_main)
  File "/cheri/source/mainline/cheribuild/pycheribuild/processutils.py", line 717, in run_and_kill_children_on_exit
    fn()
  File "/cheri/source/mainline/cheribuild/pycheribuild/__main__.py", line 248, in real_main
    target_manager.run(cheri_config)
  File "/cheri/source/mainline/cheribuild/pycheribuild/targets.py", line 431, in run
    target.execute(config)
  File "/cheri/source/mainline/cheribuild/pycheribuild/targets.py", line 127, in execute
    self._do_run(config, msg="Built", func=lambda project: project.process())
  File "/cheri/source/mainline/cheribuild/pycheribuild/targets.py", line 112, in _do_run
    func(project)
  File "/cheri/source/mainline/cheribuild/pycheribuild/targets.py", line 127, in <lambda>
    self._do_run(config, msg="Built", func=lambda project: project.process())
  File "/cheri/source/mainline/cheribuild/pycheribuild/projects/run_qemu.py", line 501, in process
    self._list_kernel_configs()
  File "/cheri/source/mainline/cheribuild/pycheribuild/projects/run_qemu.py", line 486, in _list_kernel_configs
    for conf in self._valid_kernel_configs():
  File "/cheri/source/mainline/cheribuild/pycheribuild/projects/run_qemu.py", line 482, in _valid_kernel_configs
    return self.source_project.get_kernel_configs(platform=ConfigPlatform.QEMU)
  File "/cheri/source/mainline/cheribuild/pycheribuild/projects/cross/cheribsd.py", line 1711, in get_kernel_configs
    default = super().get_kernel_configs(**filter_kwargs)
  File "/cheri/source/mainline/cheribuild/pycheribuild/projects/cross/cheribsd.py", line 1451, in get_kernel_configs
    assert config is not None, "Invalid configuration name"
AssertionError: Invalid configuration name

Attempting to run (with the various --[...]-roots set correctly, and not shown) without --list-kernels, i.e., .../cheribuild.py [...] --cheribsd-riscv64-purecap/kernel-config=CHERI-CAPREVOKE-QEMU run-riscv64-purecap, I am told

Fatal error: Dependency for run-riscv64-purecap missing: Loader/kernel is missing: /cheri/out/cornucopia-modernize/rootfs-riscv64-purecap/boot/kernel.CHERI-QEMU/kernel

If I replace --cheribsd-rsicv64-purecap with --run-riscv64-purecap/alternative-kernel (i.e., .../cheribuild.py [...] --run-riscv64-purecap/alternative-kernel=CHERI-CAPREVOKE-QEMU run-riscv64-purecap), then I am instead told

Fatal error: Selected kernel configuration CHERI-CAPREVOKE-QEMU is not available

If I happen to pass both --cheribsd-riscv64-purecap/kernel-config and --run-riscv64-purecap/alternative-kernel, I get a slightly different explosion that happens to point at a hackish edit I can make to be able to run my custom kernel again. Specifically, if I take out the attempt at a preflight check at

cheribuild/pycheribuild/projects/run_qemu.py

Lines 457 to 459 in 1aa8e94

	if self.kernel_config not in self._valid_kernel_configs():
	self.fatal("Selected kernel configuration", self.kernel_config, "is not available")
	self._list_kernel_configs()

then everything runs as I expect:

$ [...]/cheribuild.py [...] run-riscv64-purecap --run-riscv64-purecap/alternative-kernel=CHERI-CAPREVOKE-QEMU
[...]
FreeBSD 13.0-CURRENT #0 7cfc5c22594c-c337148(HEAD)-dirty: Mon Jul 12 01:50:45 UTC 2021
    daemon@af8c473f038b:/cheri/build/cornucopia-modernize/cheribsd-riscv64-purecap-build/cheri/source/cornucopia-modernize/cheribsd/riscv.riscv64c/sys/CHERI-CAPREVOKE-QEMU riscv