Skip unsupported architectures for kpet multiarch command

There are some old RHEL streams where only a subset of architectures is supported these days, but we have to build all architectures to verify the Brew builds don't get broken. Thus, the architectures variable and the kpet tree arch list don't match there.

kpet chokes if we pass it an unsupported architecture (understandibly so), so we have to ensure this does not happen and we sanitize the list to only contain the architectures we're actually running testing for.

Signed-off-by: Veronika Kabatova vkabatov@redhat.com