kpatch-build: ignores ERROR() from create-kpatch-module and create-klp-module

[joe-lawrence]

As discovered in #1203, kpatch-build continues executing if create-klp-module or create-kpatch-module sets error status.

In both cases, check_pipe_status() is called to try and catch a segfault condition (code 139), but the ERROR() macro in log.h sets EXIT_STATUS_ERROR which is not the same. This can lead to kpatch-build reporting success when an error actually occurred.

[sm00th]

check_pipe_status() handles the segfault case, but it also writes down the commands exit-code into rc variable. In case of create-diff-object call this variable is then properly checked, but neither of module create calls do that. So we don't need to touch check_pipe_status() itself, but rather add exit-status handling code after those calls.