Reduce the size of the ironic-agent ramdisk

This patch is reducing the size of the ramdisk image generated by the
ironic-agent element. It does remove extra packages (graphical stuff,
dev stuff, miscs, docs, etc...) and purges directories that are not
needed for a ramdisk (like /boot since it boots using an external
kernel)

Currently it was tested generating a Fedora 22 image and reduced the
size of the final image from 464 MB to 211MB compacted (54% decrease).

I was able to boot a VM with 1.3 GiB of ram instead of the previous 3 GiB
needed.

Change-Id: Id6333ca5d99716ccad75ea1964896acf371fa72a

elements/ironic-agent/README.rst

@@ -15,3 +15,6 @@ Beyond installing the ironic-python-agent, this element does the following:
 * When installing from source, ``python-dev`` and ``gcc`` are also installed
   in order to support source based installation of ironic-python-agent and its
   dependencies.
+
+.. note::
+   Using the ramdisk will require at least 1.5GB of ram

elements/ironic-agent/cleanup.d/99-ramdisk-create

@@ -18,7 +18,7 @@ echo "#disabled" > ./tmp/fstab.new
 sudo mv ./tmp/fstab.new ./etc/fstab
 sudo ln -s ./sbin/init ./
 
-sudo find . -path ./sys -prune -o -path ./proc -prune -o -path './tmp/*' -prune -o -print | sudo cpio -o -H newc | gzip > ${IMAGE_PATH}.initramfs
+sudo find . -path ./sys -prune -o -path ./proc -prune -o -path './tmp/*' -prune -o -path './boot/*' -prune -o -path './root/*' -prune -o -path './usr/lib/locale/*' -prune -o -path './usr/share/doc/*' -prune -o -path './usr/share/man/*' -prune -o -path './usr/share/info/*' -prune -o -path './usr/share/licenses/*' -prune -o -path './usr/share/misc/*' -prune -o -print | sudo cpio -o -H newc | gzip > ${IMAGE_PATH}.initramfs
 
 select_boot_kernel_initrd $TARGET_ROOT
 sudo cp $BOOTDIR/$KERNEL ${IMAGE_PATH}.vmlinuz

elements/ironic-agent/finalise.d/99-remove-extra-packages

@@ -0,0 +1,28 @@
+#!/bin/bash
+
+if [ "${DIB_DEBUG_TRACE:-0}" -gt 0 ]; then
+    set -x
+fi
+set -eu
+set -o pipefail
+
+# TODO(lucasagomes): optimize the ramdisk for other OSs
+if [ $DISTRO_NAME = 'fedora' ] ; then
+
+    install-packages -e kernel-debug-devel gcc fedora-logos python3 rsync sudo pykickstart grubby make genisoimage tcpdump man-db policycoreutils kbd-misc plymouth cronie
+
+    if [ $DIB_RELEASE -ge 22 ]; then
+        # Remove yum, >= F22 defaults to dnf
+        dnf remove yum -y
+        # Remove package manager cache
+        dnf clean all
+    else
+        # Remove package manager cache
+        yum clean all
+    fi
+
+    # Rebuilding the rpm database after removing packages will reduce
+    # its size
+    rpm --rebuilddb
+
+fi