Merge PR #24844 into master

* refs/pull/24844/head:
	osd: drop PGBackend::Listener::get_epoch().
	osd: massively switch to get_osdmap_epoch().
	osd: switch the return type of PG::get_osdmap().

Reviewed-by: Sage Weil <sage@redhat.com>

diff --cc src/osd/PG.cc
Simple merge

diff --cc src/osd/PG.h
Simple merge

diff --cc src/osd/PrimaryLogPG.cc
Simple merge

diff --cc src/osd/PrimaryLogPG.h
Simple merge