Improve -on-error descriptions

command/build.go

@@ -290,10 +290,7 @@ Options:
   -except=foo,bar,baz        Build all builds other than these
   -force                     Force a build to continue if artifacts exist, deletes existing artifacts
   -machine-readable          Machine-readable output
-  -on-error=abort            If the build fails, abort without cleanup
-  -on-error=ask              If the build fails, prompt for action
-  -on-error=cleanup          If the build fails, clean up and exit (the default)
-  -only=foo,bar,baz          Only build the given builds by name
+  -on-error=[cleanup|abort|ask] If the build fails do: clean up (default), abort, or ask
   -parallel=false            Disable parallelization (on by default)
   -var 'key=value'           Variable for templates, can be used multiple times.
   -var-file=path             JSON file containing user variables.

common/multistep_runner.go

@@ -135,7 +135,7 @@ func ask(ui packer.Ui, name string, state multistep.StateBag) askResponse {
 
 func askPrompt(ui packer.Ui) askResponse {
 	for {
-		line, err := ui.Ask("[C]lean up and exit, [a]bort without cleanup, or [r]etry step (build may fail even if retry succeeds)?")
+		line, err := ui.Ask("[c] Clean up and exit, [a] abort without cleanup, or [r] retry step (build may fail even if retry succeeds)?")
 		if err != nil {
 			log.Printf("Error asking for input: %s", err)
 		}

website/source/docs/command-line/build.html.md

@@ -39,9 +39,9 @@ artifacts that are created will be outputted at the end of the build.
 -   `-on-error=cleanup` (default), `-on-error=abort`, `-on-error=ask` - Selects
     what to do when the build fails.  `cleanup` cleans up after the previous
     steps, deleting temporary files and virtual machines.  `abort` exits without
-    any cleanup, but the next build may require `-force`.  `ask` presents a
-    prompt and waits for you to decide to clean up, abort, or retry the failed
-    step.
+    any cleanup, which might require the next build to use `-force`.  `ask`
+    presents a prompt and waits for you to decide to clean up, abort, or retry
+    the failed step.
 
 -   `-only=foo,bar,baz` - Only build the builds with the given
     comma-separated names. Build names by default are the names of their