crimson/osd: ignore SIGHUP

crimson/osd: ignore SIGHUP

ignore SIGHUP, as crimson does not write log messages using the
facilities offered by ceph::logging. it uses seastar::logger instead.

and seastar::logger writes to stderr, stdout and/or syslog. there is no
need to reopen the log file when the settings change.

and we do send SIGHUP to OSD processes when performing thrash tests. to
avoid killing crimson-osd processes by accident. SIGHUP is ignored.

Signed-off-by: Kefu Chai <kchai@redhat.com>