Add option --image-size.

Adds an option for --image-size, which sets the DIB_IMAGE_SIZE
environment variable.  Having the cli option makes disk-image-create
more consistent in that parameters are able to be specified via a flag
on the command line or an environment variable.  Also, you may not be
able to remember all the environment variables that you can tweak, yet
--help will tell you about the cli parameters.  Preserves the old
behavior as well where if DIB_IMAGE_SIZE is set in your environment, it
will be honored.

Change-Id: I195c9144a80ce7b8bd5809b57f2bed71a2cbdf26

bin/disk-image-create

@@ -50,6 +50,7 @@ function show_options () {
     echo "    -x -- turn on tracing"
     echo "    -u -- uncompressed; do not compress the image - larger but faster"
     echo "    -c -- clear environment before starting work"
+    echo "    --image-size size -- image size in GB for the created image"
     echo "    --image-cache directory -- location for cached images(default ~/.cache/image-create)"
     echo "    --min-tmpfs size -- minimum size in GB needed in tmpfs to build the image"
     echo "    --no-tmpfs -- do not use tmpfs to speed image build"
@@ -70,7 +71,7 @@ function show_options () {
 
 INSTALL_PACKAGES=""
 COMPRESS_IMAGE="true"
-TEMP=`getopt -o a:ho:xucnp: -l no-tmpfs,offline,help,min-tmpfs: -n $SCRIPTNAME -- "$@"`
+TEMP=`getopt -o a:ho:xucnp: -l no-tmpfs,offline,help,min-tmpfs,image-size: -n $SCRIPTNAME -- "$@"`
 if [ $? -ne 0 ] ; then echo "Terminating..." >&2 ; exit 1 ; fi
 
 # Note the quotes around `$TEMP': they are essential!
@@ -86,6 +87,7 @@ while true ; do
         -c) shift ; export CLEAR_ENV=1;;
         -n) shift; export SKIP_BASE="1";;
         -p) IFS="," read -a INSTALL_PACKAGES <<< "$2"; export INSTALL_PACKAGES ; shift 2 ;;
+        --image-size) export DIB_IMAGE_SIZE=$2; shift 2;;
         --image-cache) export DIB_IMAGE_CACHE=$2; shift 2;;
         --min-tmpfs) export DIB_MIN_TMPFS=$2; shift 2;;
         --no-tmpfs) shift; export DIB_NO_TMPFS=1;;