The configure script tries to probe whether /var/run exists when
determining the location for the pid file, which is not very nice when
doing chroot builds. Just set it explicitly to avoid the problem.
For reference, the culprit in configure.ac:
````
piddir=/var/run
if test ! -d $piddir ; then
piddir=`eval echo ${sysconfdir}`
case $piddir in
NONE/*) piddir=`echo $piddir | sed "s~NONE~$ac_default_prefix~"` ;;
esac
fi
AC_ARG_WITH([pid-dir],
[ --with-pid-dir=PATH Specify location of ssh.pid file],
...
````
Also, use the `install-nokeys` target in installPhase so we avoid
installing useless host keys into $out/etc/ssh and improve built purity
as well.