Merge pull request #6080 from clever215/wkm-master-139

rgw: modify documents and help infos' descriptions to the usage of option date when executing command "log show"

Reviewed-by: Yehuda Sadeh <yehuda@redhat.com>

diff --cc doc/man/8/radosgw-admin.rst
Simple merge

diff --cc src/rgw/rgw_admin.cc
Simple merge

diff --cc src/test/cli/radosgw-admin/help.t
Simple merge