Merge PR #22586 into master

Merge PR #22586 into master

* refs/pull/22586/head:
	global/signal_handler: one less frame of context
	global/signal_handler: write crash dumps to /var/lib/ceph/crash/$uuid/
	common/ceph_context: add "assert" and "abort" asok commands
	common/assert: record assert info in g_assert_* globals
	common: add crash_dir option
	common/assert: get rid of duplicate log dump from assert handler
	common/BackTrace: add dump()
	log: do not discard recent after dumping it
	debian,rpm: /var/lib/ceph/crash