doc: Added connectivity section. Updated doc with glossary terms.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Updated disk syntax. Updated text with glossary terms.

fixes: #4933

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Updated doc for connectivity. Updated text with glossary terms.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
Merge branch 'master' of https://github.com/ceph/ceph