Reland "cros_run_unit_tests: Add --host option to run tests on host"

This is a reland of 295df5d587d616eef10a012a9715fdfb9923e9c3

This reland contains a fix for b:208651520 which triggered the revert.
cros_generate_sysroot writes config (etc/make.conf.board_setup) to an
empty sysroot, but with this CL now needs to also write etc/make.conf so
the generated config can be read.

BUG=b:193915549
TEST=pass CQ, run cros_generate_sysroot

Original change's description:
> Reland "cros_run_unit_tests: Add --host option to run tests on host"
>
> This is a reland of da20116575cb305bff6d08fe6aa0b04bdf5b34f3
>
> Ok to reland now as underlying issue for revert has been resolved by
> chromium:3256026, chromium:3253802, and chromium:3253130.
>
> Original change's description:
> > cros_run_unit_tests: Add --host option to run tests on host
> >
> > Better support is needed for running host package unit tests.  This adds
> > that functionality to the cros_run_unit_tests command with the --host
> > option.  Aligned with the existing behavior, specifying only the --host
> > option tests all installed packages in virtual/target-sdk.  Existing
> > additional cros_run_unit_tests options are supported in this mode as
> > well.
> >
> > BUG=b:193915549
> > TEST=pass CQ
> >
> > Change-Id: I0b20332c3b09c9faac3500f2ed813d916f701f36
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3188310
> > Reviewed-by: Mike Frysinger <vapier@chromium.org>
> > Reviewed-by: Lizzy Presland <zland@google.com>
> > Commit-Queue: Sloan Johnson <sloanjohnson@google.com>
> > Tested-by: Sloan Johnson <sloanjohnson@google.com>
>
> Bug: b:193915549
> Cq-Depend: chromium:3256026
> Change-Id: Ifa13db9fbcc36497985506bd6ff2b1cec18ac34d
> Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3256201
> Tested-by: Sloan Johnson <sloanjohnson@google.com>
> Commit-Queue: Sloan Johnson <sloanjohnson@google.com>
> Reviewed-by: Mike Frysinger <vapier@chromium.org>
> Reviewed-by: Lizzy Presland <zland@google.com>

Change-Id: I8eb06d784ccb25329f8a1ab3ccb813581c858329
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3312069
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Tested-by: Sloan Johnson <sloanjohnson@google.com>
Commit-Queue: Sloan Johnson <sloanjohnson@google.com>
diff --git a/scripts/cros_run_unit_tests_unittest.py b/scripts/cros_run_unit_tests_unittest.py
index 5696729..29e17a9 100644
--- a/scripts/cros_run_unit_tests_unittest.py
+++ b/scripts/cros_run_unit_tests_unittest.py
@@ -16,5 +16,5 @@
 
   def testNonEmptyPackageSet(self):
     """Asserts that the deps of a known package are non-empty"""
-    self.assertTrue(cros_run_unit_tests.determine_board_packages(
+    self.assertTrue(cros_run_unit_tests.determine_packages(
         '/', ('virtual/implicit-system',)))