log: do not repeat errors to stderr

log: do not repeat errors to stderr

If we get an error writing to the log, log it only once to stderr.
This avoids generating, say, 72 GB of ENOSPC errors in
teuthology.log when /var/log fills up.

Fixes: #14616
Signed-off-by: Sage Weil <sage@redhat.com>
(cherry picked from commit d9ac0474b864afda58a44b9012cca4bbc6aaf509)

Conflicts:
	src/log/Log.cc (drop m_uid and m_gid which are not used in hammer;
	order of do_stderr, do_syslog, do_fd conditional blocks is reversed in
	hammer; drop irrelevant speed optimization code from
	5bfe05aebfefdff9022f0eb990805758e0edb1dc)