tmpfiles: fix detection of unitialized-/etc

tmpfiles: fix detection of unitialized-/etc

In 6ec4c852c910b1aca649e87ba3143841334f01fa I changed specifier_machine_id() to
return EUNATCH, but the code catching in tmpfiles wasn't adjusted.

Instead of translating errors at various levels, let the "original" errno value
(whatever was returned by the low-level reading function) propagate all the way
to the logging function, and only check which errnos to suppress there. This
makes it easier to follow the flow of data through all the layers. Also, we
don't need to provide wrapper functions for each place where we want to do the
supression.

The common set of errnos that have similar meaning are are caught using
ERRNO_IS_NOINFO(). It is more managable to use a wider net than to figure out
which errors could be returned in specific cases.