minor tweaks in spec file

always require system-release.  It's provided by fedora-release,
redhat-release, and centos-release.

Update the summary for ovirt-node-tools

Change-Id: I331e4a48f3ab01bbc2b153d1420a91de3f2a2f85
Signed-off-by: Mike Burns <mburns@redhat.com>