Use $DISTRO_NAME instead of local lsb_release

The $DISTRO_NAME var is now set in all of the OS elements
in environment.d.  This patch removes the call to
lsb_release and instead uses the $DISTRO_NAME variable.

Change-Id: I7088eb88b6a3611fef5a21a6b62975876549465f

elements/base/pre-install.d/03-baseline-tools

@@ -4,11 +4,8 @@
 set -eu
 set -o pipefail
 
-# If lsb_release is missing, just do nothing.
-DISTRO=`lsb_release -si` || true
-
-case $DISTRO in
-    'Ubuntu'|'Debian')
+case $DISTRO_NAME in
+    'ubuntu'|'debian')
         # Note: add-apt-repository would be nice for RPM platforms too - so when we
         # need something like it, create a wrapper in dpkg/bin and fedora/bin.
         apt-get -y update

elements/ramdisk/install.d/20-install-dhcp-client

@@ -2,8 +2,6 @@
 set -eux
 set -o pipefail
 
-DISTRO=`lsb_release -si` || true
-
-if [ "openSUSE project" = "$DISTRO" ]; then
+if [ "opensuse" = "$DISTRO_NAME" ]; then
     install-packages dhcp-client
 fi