build: update rpmbuild .spec file

Rename the package to iojs.  No Conflicts: header is necessary because
the package was already marked as conflicting with the Fedora nodejs
package.

PR-URL: https://github.com/iojs/io.js/pull/71
Reviewed-By: Rod Vagg <rod@vagg.org>
build: rename rpmbuild .spec file

Rename the .spec file from node.spec to iojs.spec and update the build
script.  Done as a separate commit to not obscure the changes from the
previous commit.

PR-URL: https://github.com/iojs/io.js/pull/71
Reviewed-By: Rod Vagg <rod@vagg.org>