Ant RPM build configuration is modified such that:

 - rpmbuild arch of x86_64 is now default.  This will require a
   change to the Ignite's Bamboo to specify a 64bit JRE to bundle
 - the rpmbuild arch logic is simplified and one can now specify
   which arch to build for by setting `-Drpmbuild.arch=<arch>`
 - the resulting RPM filenames are changed, such to allow upgrades
   between alpha builds, beta/rc builds and GA builds without
   having to `rpm --force` these.  See note below on the new
   RPM filenames.
 - the changelog field in the RPM will contain the hash of the
   last commit in the local repository `git rev-parse --short HEAD`
 - A new `git.revision` Ant target is introduced so support the
   inclusion of this in the build metadata

New RPM filenames:
    For General Releases we get x.y.z-1
    For Alpha builds we get     x.y.z-0.1.{YYYYMMDD}alpha
    For Beta/RC builds we get   x.y.z-0.2.(beta|rc)