xapi: include an empty /usr/share/xapi/packages/iso
xapi: it turns out that RPM ignores \-separated lines by silently skipping them
xapi: generate the xapissl.conf from the init.d script as upstream intended

This is important because xapi tells xapissl what addresses to accept on.
xapi: add a pam configuration suitable for CentOS

I verified that a non-root user cannot execute xe commands without
re-authenticating as root.
Merge pull request #74 from djs55/make-srpms

Make srpms