arch-run: generate errata when no environ is provided

Provide a table mapping errata to minimum kernel versions and
a function that will use the host's kernel version to determine
the values for each errata variable. These errata variables, with
values based on the host kernel, are now provided to all unit
tests by default, if no environ is provided. Errata variables
passed from the run script environment still take precedence.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>