Fallback to file logging if system loggers not available

[vholer]

If may happen the logging via systemd-cat or even logger is not available. The contextualization should fallback to the log on its own with a syslog line format. Also, the logging function should have neutral return code no matter if the function succeeds or fails.

addon-context-linux/src/usr/sbin/one-contextd

Lines 56 to 68 in 44f01e6

	logger -t "${SYSLOG_TAG}" \
	-p "${SYSLOG_FACILITY}.${1}" \
	"${2}" 2>/dev/null
	elif [ "${1}" != 'debug' ]; then
	local _txt="$(date "+%b %d %T") $(hostname -s) ${SYSLOG_TAG}: ${2}"
	local _log=/var/log/messages
	if [ -f /var/log/syslog ]; then
	_log=/var/log/syslog
	fi
	echo "${_txt}" >>"${_log}" 2>/dev/null