[#51148043] Choose sigar file as per system arch

If lib-sigar-<arch>-<system>.so that is copied over for deb pkg isnt
correct then results in build failure (even if all .so files are
copied). To fix this we are now using the DEB_BUILD_ARCH to get the
correct architecture.
[#51148043] Pulled {post/pre}{inst/rm} steps from upstream for es