Bump to 0.20.6 and fix sigar bindings

I found your ES package useful so I bumped it to the latest 0.20.x version. I also fixed the inclusion of the native sigar bindings by removing the BuildArch declaration, (using 'noarch' means '%ifarch x86_64' will never match) so the OS-level statistics now work.

Obviously ES themselves maintain some 0.90.x RPMs but I'm not feeling brave to upgrade just yet.