Merge pull request #3867 from wonzhq/fiemap

FileStore: fiemap implementation using SEEK_HOLE/SEEK_DATA

Reviewed-by: Haomai Wang <haomaiwang@gmail.com>
Reviewed-by: Sage Weil <sage@redhat.com>

diff --cc src/common/config_opts.h
Simple merge

diff --cc src/os/FileStore.cc
Simple merge

diff --cc src/os/FileStore.h
Simple merge