Fix $DISTRO_NAME usage for centos7 element

In both of the changed files in this patch, the $DISTRO_NAME usage
is checking against "centos".  The valid value for the centos7
element for $DISTRO_NAME is "centos7"[1].

[1] http://git.io/8IvuTw

Change-Id: I0c4a4b2ecf87c7a9283d10071f6feb494a6c716a
Merge "Fix $DISTRO_NAME usage for centos7 element"