systemd-python: attach fields to JournalHandler, add SYSLOG_IDENTIFIER
systemd-python: attach fields to JournalHandler, add SYSLOG_IDENTIFIER

Arbitrary fields can be attached at the level of the handler,
and they'll be sent with all messages from this handler.

This facility is used to attach SYSLOG_IDENTIFIER to all messages,
since otherwise journald attaches SYSLOG_IDENTIFIER=python or
something similar, which is completely useless.

systemd/python-systemd,keszybz/python-systemd,Awesense/python-systemd,again4you/python-systemd,again4you/python-systemd,systemd/python-systemd,Awesense/python-systemd,keszybz/python-systemd,Awesense/python-systemd