Improve RPM building to handle "Version" and name the tarball

[nkadel]

The RPM building setup has some issues.

• The "Version" is not set in amazon-efs-utils.spec
  • The .spec file could be generated with an amazon-efs-utils.spec.in, and built with a VERSION in the Makefile
• The generated tarball is named amazon-efs-utils.tar.gz, which does not hint at the version
  • The tarball can be generated with a VERSION in the Makefile
• The "make rpm-only" option depends on "make tarball"
  • That could be a Makefile option
• The "rmbuild" options don't have to have the source files copied into the "dist/rpmbuild" directory, they can use:
  • rpmbuild --define '_sourcedir $(PWD)'

With all that in place, it's be possible to build RPMs more completely and consistently.

[nkadel]

See Pull Request 96.

[bahildebrand]

@nkadel thanks for the feedback. We'll have someone take a look at this.