[PATCH] CI: workaround broken selinux+docker interaction in yocto

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

`cp --preserve=xattr` doesn't work in docker when SELinux is enabled. It
tries to set the "security.selinux" xattr, but SELinux (or overlay fs?)
denies it.
Workaround it by skipping selinux.selinux xattr copying.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
---
Tested here:
https://gitlab.com/xen-project/people/marmarek/xen/-/jobs/7386198058

But since yocto container fails to build, it isn't exactly easy to apply
this patch...
"kirkstone" branch of meta-virtualization seems to target Xen 4.15 and
4.16, so it isn't exactly surprising it fails to build with 4.19.

I tried also bumping yocto version to scarthgap (which supposedly should
have updated pygrub patch), but that fails to build for me too, with a
different error:

    ERROR: Layer 'filesystems-layer' depends on layer 'networking-layer', but 
this layer is not enabled in your configuration
    ERROR: Parse failure with the specified layer added, exiting.
    ...
    ERROR: Nothing PROVIDES 'xen-image-minimal'. Close matches:
      core-image-minimal
      core-image-minimal-dev
    Parsing of 2472 .bb files complete (0 cached, 2472 parsed). 4309 targets, 
101 skipped, 0 masked, 0 errors.
---
 automation/build/yocto/yocto.dockerfile.in | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/automation/build/yocto/yocto.dockerfile.in 
b/automation/build/yocto/yocto.dockerfile.in
index fbaa4e191caa..600db7bf4d19 100644
--- a/automation/build/yocto/yocto.dockerfile.in
+++ b/automation/build/yocto/yocto.dockerfile.in
@@ -68,6 +68,10 @@ RUN locale-gen en_US.UTF-8 && update-locale 
LC_ALL=en_US.UTF-8 \
 ENV LANG en_US.UTF-8
 ENV LC_ALL en_US.UTF-8
 
+# Workaround `cp --preserve=xattr` not working in docker when SELinux is
+# enabled
+RUN echo "security.selinux skip" >> /etc/xattr.conf
+
 # Create a user for the build (we don't want to build as root).
 ENV USER_NAME docker-build
 ARG host_uid=1000
-- 
2.45.2