dmeventd: separate dm and dmeventd logging

dmeventd: separate dm and dmeventd logging

Ensure different logging function for dmeventd.c logging
and dm and lvm library.

We can recognize we want to show every log_info() and
log_notice() message from dmeventd.c code while not
exposing those from libdm/libdevmapper-event

Also switch to use log with errno - it's not changing
anything and doesn't bring any more features yet to dmeventd
logging but we just properly pass dm_errno_or_class properly
through the whole code stack for possible future use
(i.e. support of class logging for dmeventd).