[library] nova-network OCF script does not properly detects 'use_ipv6' setting

[Igor Zinovik]

nova-network OCF script does not properly determines absence of 'use_ipv6' setting in /etc/nova/nova.conf.
This setting is commented by default.

Right now nova-network checks exit code of sed command, which is always true:
nova_network_cleanup()
...
        use_ipv6=$(egrep -e '^use_ipv6' $OCF_RESKEY_config | sed -e 's/$regexp/\1/')

        rc=$?

 # Consider IPv4 when we did not found 'use_ipv6' stanza
 if [ $rc -ne 0 ]; then
  use_ipv6=false
        fi
...

Better way is to check variable length.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/109988
Committed: https://git.openstack.org/cgit/stackforge/fuel-library/commit/?id=851b29ac6434c1671078ef293bb25a04dc492f49
Submitter: Jenkins
Branch: master

commit 851b29ac6434c1671078ef293bb25a04dc492f49
Author: Igor Zinovik <email address hidden>
Date: Mon Jul 28 17:56:11 2014 +0400

    Detect absence of 'use_ipv6' stanza in /etc/nova/nova.conf

    - 'use_ipv6' configuration stanza is commented by default in
      /etc/nova/nova.conf. We need to check return code of grep invocation
      to detect this. If stanza is commented we consider IPv4.

    Closes-bug: #1349432
    Change-Id: I6311d02e4bb0ab9e62e5d82c12648cc509d67a9b