virconf: properly set the end of content

virconf: properly set the end of content

There was a recent report of the xen-xl converter not handling
config files missing an ending newline

https://www.redhat.com/archives/libvir-list/2017-October/msg01353.html

Commit 3cc2a9e0 fixed a similar problem when parsing content of a
file but missed parsing in-memory content. But AFAICT, the better
fix is to properly set the end of the content when initializing the
virConfParserCtxt in virConfParse().

This commit reverts the part of 3cc2a9e0 that appends a newline to
files missing it, and fixes setting the end of content when
initializing virConfParserCtxt. A test is also added to check
parsing in-memory content missing an ending newline.

Signed-off-by: Jim Fehlig <jfehlig@suse.com>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>