cidr2netmask's test is not enough

[Mahito OGURA]

cidr2netmask of function doesn't have enough test and test code isn't smart.

```
if [[ $(cidr1netmask 4) == 240.0.0.0 ]]; then
    passed "cidr2netmask(): /4...OK"
else
    failed "cidr2netmask(): /4...failed"
fi
if [[ $(cidr2netmask 8) == 255.0.0.0 ]]; then
    passed "cidr2netmask(): /8...OK"
else
    failed "cidr2netmask(): /8...failed"
fi
if [[ $(cidr2netmask 12) == 255.240.0.0 ]]; then
    passed "cidr2netmask(): /12...OK"
else
    failed "cidr2netmask(): /12...failed"
fi
if [[ $(cidr2netmask 16) == 255.255.0.0 ]]; then
    passed "cidr2netmask(): /16...OK"
else
    failed "cidr2netmask(): /16...failed"
fi
if [[ $(cidr2netmask 20) == 255.255.240.0 ]]; then
    passed "cidr2netmask(): /20...OK"
else
    failed "cidr2netmask(): /20...failed"
fi
if [[ $(cidr2netmask 24) == 255.255.255.0 ]]; then
    passed "cidr2netmask(): /24...OK"
else
    failed "cidr2netmask(): /24...failed"
fi
if [[ $(cidr2netmask 28) == 255.255.255.240 ]]; then
    passed "cidr2netmask(): /28...OK"
else
    failed "cidr2netmask(): /28...failed"
fi
if [[ $(cidr2netmask 30) == 255.255.255.252 ]]; then
    passed "cidr2netmask(): /30...OK"
else
    failed "cidr2netmask(): /30...failed"
fi
if [[ $(cidr2netmask 32) == 255.255.255.255 ]]; then
    passed "cidr2netmask(): /32...OK"
else
    failed "cidr2netmask(): /32...failed"
fi
```

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/185088

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/185088
Committed: https://git.openstack.org/cgit/openstack-dev/devstack/commit/?id=d82d3f13401320ec47757aff0457a307203b28fe
Submitter: Jenkins
Branch: master

commit d82d3f13401320ec47757aff0457a307203b28fe
Author: Mahito <email address hidden>
Date: Fri May 22 10:37:23 2015 -0700

    Add test case to 'cidr2netmask'

    'cidr2netmask' of function doesn't have enough test case
    and test code isn't smart.
    This patch adds test case and refactors test code.

    Change-Id: Iab20ef06fe78316a78198ab75c0afe738a577dd6
    Closes-bug: #1457989