keepalive: work around slight deficiency in vcr
VCR's response type doesn't define the will_close attribute. Let's
just have keepalive default to closing the socket if the will_close
attribute is missing.
Differential Revision: https://phab.mercurial-scm.org/D4599
$ echo "[extensions]" >> $HGRCPATH
$ echo "mq=" >> $HGRCPATH
$ hg init
$ echo 'base' > base
$ hg ci -Ambase
adding base
$ hg qnew -mmqbase mqbase
$ hg qsave
$ hg qrestore 2
restoring status: hg patches saved state