tests: merge last/ and utmpdump/ into new utmp/ dir

We want to prepare and simplify utmp sepcific fixes.

Signed-off-by: Ruediger Meier <ruediger.meier@ga-group.nl>
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: create last test data for exotic utmp sizes

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

Also we add/update some test text data which matchs our existing
binary data.

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>