labs: verify MD5 checksum for Linux ISO image

Verify the MD5 checksum of the Linux distribution's ISO image before
trying to use it. Image corruption happens, and the resulting problems
are not always easy to diagnose.

Change-Id: I92852a28392002d4fcd64898453086d5920d0ef1

labs/lib/osbash/lib.ubuntu-14.04-server-amd64

@@ -8,6 +8,7 @@
 #-------------------------------------------------------------------------------
 
 readonly ISO_URL=http://releases.ubuntu.com/14.04/ubuntu-14.04.1-server-amd64.iso
+readonly ISO_MD5=ca2531b8cd79ea5b778ede3a524779b9
 
 readonly _PS_ssh=http://git.openstack.org/cgit/openstack/training-guides/plain/labs/lib/osbash/netboot/preseed-ssh.cfg
 readonly _PS_vbadd=http://git.openstack.org/cgit/openstack/training-guides/plain/labs/lib/osbash/netboot/preseed-vbadd.cfg

labs/lib/osbash/virtualbox.install_base

@@ -1,5 +1,26 @@
 # This bash library contains the main function that creates the base disk.
 
+function check_md5 {
+    local file=$1
+    local csum=$2
+    local md5exe
+    if ! md5exe=$(which md5sum); then
+      # On Mac OS X, the tool is called md5
+      if ! md5exe=$(which md5); then
+        echo >&2 "Neither md5sum nor md5 found. Aborting."
+        exit 1
+      fi
+    fi
+    echo >&2 -n "Verifying ISO image MD5 checksum: "
+    if $md5exe "$file" | grep -q "$csum"; then
+        echo >&2 "okay."
+    else
+        echo >&2 "failed."
+        echo >&2 "Aborting. Please fix or remove the ISO image."
+        exit 1
+    fi
+}
+
 function vm_install_base {
     local base_disk=$1
     local base_build_disk=$DISK_DIR/tmp-disk.vdi
@@ -32,6 +53,9 @@ function vm_install_base {
     fi
 
     echo >&2 -e "Install ISO:\n\t$INSTALL_ISO"
+
+    ${OSBASH:-:} check_md5 "$INSTALL_ISO" "$ISO_MD5"
+
     $VBM storageattach "$vm_name" \
         --storagectl IDE \
         --port 0 \