rs.stepDown's parameter is optional

Signed-off-by: Sam Kleinman <samk@10gen.com>
DOCS-2214: replSetGetStatus fix
DOCS-2192: slavedelay is lowercase
add and view roles, changes to 'required access' in ref docs"

Signed-off-by: Sam Kleinman <samk@10gen.com>
edits to privlege modification tutorials