[sahara-image-elements] Check distro name from DISTRO_NAME

[Denis Egorenko]

Now we check distr name via using variable "distro", for example:
https://github.com/openstack/sahara-image-elements/blob/master/elements/hadoop/post-install.d/40-setup-hadoop#L40
https://github.com/openstack/sahara-image-elements/blob/master/elements/hadoop-cdh/post-install.d/40-setup-hadoop#L11

Let's use DISTRO_NAME variable, which is include in each system element:
https://github.com/openstack/diskimage-builder/blob/master/elements/ubuntu/environment.d/10-ubuntu-distro-name.bash#L1
https://github.com/openstack/diskimage-builder/blob/master/elements/centos/environment.d/10-centos6-distro-name.bash#L1
https://github.com/openstack/diskimage-builder/blob/master/elements/fedora/environment.d/10-fedora-distro-name.bash#L1

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/168107

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/168107
Committed: https://git.openstack.org/cgit/openstack/sahara-image-elements/commit/?id=db50f5ba97a163f975fa8625839deb8e438f3b7b
Submitter: Jenkins
Branch: master

commit db50f5ba97a163f975fa8625839deb8e438f3b7b
Author: Denis Egorenko <email address hidden>
Date: Thu Mar 26 21:45:30 2015 +0400

    Check distro name from DISTRO_NAME

    Use default 'DISTRO_NAME' variable for check which distro is use
    for current image build

    Change-Id: Ieba71733fbcd554a1c7416efb0c4b740939d06a8
    Closes-bug: #1436807