Add a new break on error

A user running di-b several times while developing an element may not
want to drop to a shell in all cases but may only want to do so if one
of their in target hooks failed.

This patch gives them the ability to do so, If break=after-error is set
then a user will be provided a in target shell taking over from where the
last failed command left off.

Change-Id: Ia2f7ac4c21b64b971f87f4ae9cb867981b13eb5e

README.md

@@ -326,6 +326,8 @@ comma-delimited string. Some examples:
 * break=after-first-boot,before-pre-install will break after the first-boot
   hooks and before the pre-install hooks.
 
+* break=after-error will break after an error during a in target hookpoint.
+
 Images are built such that the Linux kernel is instructed not to switch into
 graphical consoles (i.e. it will not activate KMS). This maximises
 compatibility with remote console interception hardware, such as HP's iLO.

bin/disk-image-create

@@ -15,7 +15,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
-set -e
+set -eE
 
 # Prevent perl from complaining a lot, but also remove any unexpected side-effects
 # of $LANG varying between build hosts

lib/img-functions

@@ -78,7 +78,9 @@ function run_d_in_target () {
       mkdir -p $DIB_CCACHE_DIR
       sudo mount --bind $DIB_CCACHE_DIR $TMP_MOUNT_PATH/tmp/ccache
       check_break before-$1 run_in_target bash
+      trap "check_break after-error run_in_target bash" ERR
       run_in_target dib-run-parts /tmp/in_target.d/$1.d
+      trap - ERR
       check_break after-$1 run_in_target bash
       sudo umount -f $TMP_MOUNT_PATH/tmp/in_target.d
       sudo rmdir $TMP_MOUNT_PATH/tmp/in_target.d