tests: skip utmpdump tests for exotic archs

We introduce utmp_functions.sh and skip tests if size of utmp struct
does not match our wtmp test data.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
tests: provide missing test data for "last" on exotic archs

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
tests: add utmpdump-circle test (arch independent)

This one is a completely arch independent conversion round:
  text -> bin -> text -> bin

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
tests: split last into dns and nodns subtests

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
tests: skip some last tests if no dns support

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>