The current "redhat" os family omits RHEL7. The rhel7 element has the
corresponding $DISTRO_NAME set in environment.d. This patch adds rhel7
so a pkg-map json file using "redhat" for the os family will work the
same as rhel, centos and fedora.
Change-Id: If6b4cbba618167669a499e6121f234942ca9367a
Adds a new pkg-map element which can be used to install
packages based on an in element 'pkg-map' JSON config
file format.
As part of this change we expose DIB's IMAGE_ELEMENT variable
so that we can have access to the element names which are being
installed in a clean manner.
This change is intended to decouple elements from DIB
and allow new elements to support multiple distributions
(with various package naming schemes) without having to
constantly maintain DIB's various bin/map-packages files.
Change-Id: Ic0a061995e2ae708c95a535cba6237bff58f7d93