rbdmap: add manpage

[smithfarm]

http://tracker.ceph.com/issues/15212 Fixes: #15212

Signed-off-by: Nathan Cutler ncutler@suse.com

[b-ranto]

We could use the basic usage info, here. I.e. rbdmap map | unmap.

[smithfarm]

While it is true that it is usually run by init system, a user can also easily run it to achieve the same thing without having to have it run every time a computer starts -- that is why I originally kept it as a script in /usr/bin.

Alternatively, we could skip creating the man page altogether and move the script to /usr/lib/... (libexecdir). I'm not sure how useful the standalone script in bindir is and it depends mostly on that.

If there is a reasonable use case for running it manually (and I think there is), we should keep it where it is. I revamped the manpage a little - can you take another look?

[b-ranto]

I also think there is a valid use case for this being in bindir (well, that is why I originally put it there). With the recent changes to the wording and after mentioning map/unmap in the man page, lgtm,