Make iscsi-boot element support centos 8

This patch makes iscsi-boot element support not only just
DISTRO_NAME centos7 but also centos and centos-minimal.

Change-Id: I8db8b01f35b2e572666badd8d2316d24a5e4287a

diskimage_builder/elements/iscsi-boot/README.rst

@@ -3,7 +3,7 @@ iscsi-boot
 ==========
 Handles configuration for the disk to be capable of serving as
 a remote root filesystem through iSCSI. Currently, this element
-can configure Ubuntu/Debian images and CentOS7 images.
+can configure Ubuntu/Debian images and CentOS images.
 
 It performs the following actions:
 
@@ -13,7 +13,7 @@ For Ubuntu/Debian images:
     ``ISCSI_AUTO=true`` within it.
   * Updates the initramfs to apply the changes.
 
-For CentOS7 images:
+For CentOS images:
   * Required ``dracut-regenerate`` element when performs ``disk-image-create``.
   * Updates ``network`` and ``iscsi`` into ``dracut-regenerate`` during
     pre-installs.

diskimage_builder/elements/iscsi-boot/environment.d/open-iscsi-config

@@ -1,4 +1,4 @@
-if [[ $DISTRO_NAME = "centos7" ]]; then
+if [[ $DISTRO_NAME =~ "centos" ]]; then
 
     DIB_DRACUT_ENABLED_MODULES+="
 - name: network

diskimage_builder/elements/iscsi-boot/extra-data.d/50-check-dracut-regenerate

@@ -6,7 +6,7 @@ fi
 set -eu
 set -o pipefail
 
-if [[ $DISTRO_NAME = "centos7" ]]; then
+if [[ $DISTRO_NAME =~ "centos" ]]; then
     eval declare -A image_elements=($(get_image_element_array))
     if [[ ! "${image_elements[@]}" =~ "dracut-regenerate" ]]; then
         echo "The dracut-regenerate element is required!"

diskimage_builder/elements/iscsi-boot/finalise.d/51-open-iscsi-config

@@ -7,7 +7,7 @@ fi
 set -eu
 set -o pipefail
 
-if [[ $DISTRO_NAME = "centos7" ]]; then
+if [[ $DISTRO_NAME =~ "centos" ]]; then
     sed -i -E 's/(GRUB_CMDLINE_LINUX_DEFAULT=")(.+)(")/\1\2 rd.iscsi.firmware=1"/' /etc/default/grub
     grub2-mkconfig -o /boot/grub2/grub.cfg
 fi