Jiri Denemark reported an instance of bootstrapping libvirt
failing when run inside a sandbox, traced to rpm trying to
access /var/ which was not permitted by the sandbox.

Alex Jia reported that 0.9.8-rc1 failed to bootstrap if patch(1)
is not installed.

* bootstrap.conf (buildreq): Avoid rpm call if python-config
exists.  Also, require patch, in case we have gnulib-local diffs.