Merge PR #24057 into master

* refs/pull/24057/head:
	src/common: add a unit test (bufferlist.sha1())
	osd, src/common: return sha1 value if zero-length buffer.
	src/common/buffer.cc: remove unnecessary copy in sha1()

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

diff --cc src/common/buffer.cc
Simple merge

diff --cc src/include/buffer.h
Simple merge

diff --cc src/test/bufferlist.cc
Simple merge