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
#require docutils gettext
$ $TESTDIR/check-gendoc pt_BR
checking for parse errors