Description of problem:
Node upgrade copies over /etc/redhat-release which in some cases can cause confusion. In case of upgrade from RHEL 7.2 to 7.3 the file still contains 7.2 version.

Version-Release number of selected component (if applicable):
rhvh-4.0-0.20170104

How reproducible:
100%

Steps to Reproduce:
1. Modify /etc/redhat-release
2. proceed with upgrade

Actual results:
/etc/redhat-release changes are kept.

Expected results:
New information is included

Additional info:

[root@ng01 ~]# cat /etc/redhat-release /etc/os-release 
Red Hat Enterprise Linux release 7.2
NAME="Red Hat Enterprise Linux"
VERSION="7.3"
VERSION_ID="7.3"
ID="rhel"
ID_LIKE="fedora"
VARIANT="Red Hat Virtualization Host"
VARIANT_ID="ovirt-node"
PRETTY_NAME="Red Hat Virtualization Host 4.0 (el7.3)"
ANSI_COLOR="0;31"
CPE_NAME="cpe:/o:redhat:enterprise_linux:7.3:GA:hypervisor"
HOME_URL="https://www.redhat.com/"
BUG_REPORT_URL="https://bugzilla.redhat.com/"

# FIXME
REDHAT_BUGZILLA_PRODUCT="Red Hat Virtualization"
REDHAT_BUGZILLA_PRODUCT_VERSION=7.3
REDHAT_SUPPORT_PRODUCT="Red Hat Virtualization"
REDHAT_SUPPORT_PRODUCT_VERSION=7.3