Properly terminate the response to the manager Ping action.

In passing, correct the formatting of the Timestamp attribute so that there is a
space after the colon and before the value.

(closes issue #15861)
Reported by: Ivan


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@217408 65c4cc65-6c06-0410-ace0-fbb531ad65f3