Previously the first run-vmtest action step would always search for
vmlinux image in KERNEL_ROOT, and then copy it to path specified by
inputs.vmlinuz

However, the caller may want to pass vmlinux image directly.

Change this behavior: search only inputs.vmlinuz was not passed.

Signed-off-by: Ihor Solodrai <[email protected]>

Various changes in the scripts aimed to make run-vmtest action usable
by libbpf/libbpf workflows:

* Change how ALLOWLIST and DENYLIST are set up. A script executing in
  qemu (vmtest) is now expecting a single $ALLOWLIST_FILE and
  $DENYLIST_FILE which are parsed by read_lists as usual. This change
  makes it easier for an action caller to modify the lists, as they are
  often composed from a number of files.

* Update vmtest init command (executed in qemu before the tests), to
  create a link from /boot to vmlinux being tested. This is necessary
  when older kernels are tested.

* Allow some env variables to be defined outside of the scripts to
  give the caller more control over the action. That is, before
  setting a default value, check if the variable is set.

* Remove env vars like $THISDIR, $PROJECT_NAME etc. in favor of
  $GITHUB_ACTION_PATH, $GITHUB_WORKSPACE and $KERNEL_ROOT

* Move selftests running scripts from ci/vmtest to run-vmtest, so that
  they are local to the action

Signed-off-by: Ihor Solodrai <[email protected]>

Adjust run-vmtest scripts so that the action is callable from
libbpf/libbpf, particularly with pre-built kernels.

More environment variables can now be set by a caller to direct the
scripts behavior: SELFTESTS_BPF, VERISTAT_CONFIGS, VMLINUX, VMLINUZ

A symlink to standard vmlinux location is created before vmtest is
executed to accomodate older kernels.

The command passed tp vmtest is refactored, separating generic vmtet
init and VMTEST_SCRIPT execution.

Search and processing of json test summaries is now noop in case when
no summaries are found.

Signed-off-by: Ihor Solodrai <[email protected]>

FETCH_DEPTH now controls how to get linux source. If it's 0, the
snapshot is searched for and downloaded if found.  Otherwise git clone
--depth $FETCH_DEPTH is executed, and .git is preserved.

Signed-off-by: Ihor Solodrai <[email protected]>

Changes in action inputs:
  * kernel-root is now a required input
  * kernel, kbuild-output and max-make-jobs are removed

kernel-root input is required, because to build selftests
one must to clone a kernel source tree first.

The build script behavior can be directed more granularly with env
variables:
  * KBUILD_OUTPUT now defaults to the kernel-root
  * VMLINUX_BTF now can be set externally
  * MAX_MAKE_JOBS can be set as env variable if desired

Preparation script logic is removed: the rationale is that the caller
is responsible for setting up required environment before building.

Signed-off-by: Ihor Solodrai <[email protected]>

Introduce CACHED_KERNEL_BUILD variable and change download/build steps
to make use of the cached incremental build on libbpf/ci workflows.

Change parameters passed to build-selftests.

Add a step preparing allow/denylist before running vmtest.

Signed-off-by: Ihor Solodrai <[email protected]>