bot_update: make --output_json required in script invocation.

It's already set by recipe, so this should have 0 difference in prod.

R=iannucci@chromium.org

Bug:
Change-Id: I1e1129b9748d6647e45eb26892c8e892019fe088
Reviewed-on: https://chromium-review.googlesource.com/769164
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>

recipes/recipe_modules/bot_update/resources/bot_update.py

@@ -1003,7 +1003,7 @@ def parse_args():
                    help=('Deprecated.'))
   parse.add_option('--clobber', action='store_true',
                    help='Delete checkout first, always')
-  parse.add_option('--output_json',
+  parse.add_option('--output_json', required=True,
                    help='Output JSON information into a specified file')
   parse.add_option('--no_shallow', action='store_true',
                    help='Bypass disk detection and never shallow clone. '
@@ -1085,8 +1085,6 @@ def prepare(options, git_slns, active):
   step_text = '[%dGB/%dGB used (%d%%)]' % (used_disk_space_gb,
                                            total_disk_space_gb,
                                            percent_used)
-  if not options.output_json:
-    print '@@@STEP_TEXT@%s@@@' % step_text
   shallow = (total_disk_space < SHALLOW_CLONE_THRESHOLD
              and not options.no_shallow)
 
@@ -1148,7 +1146,6 @@ def checkout(options, git_slns, specs, revisions, step_text, shallow):
       ensure_no_checkout(dir_names, options.cleanup_dir)
       gclient_output = ensure_checkout(**checkout_parameters)
   except PatchFailed as e:
-    if options.output_json:
     # Tell recipes information such as root, got_revision, etc.
     emit_json(options.output_json,
               did_run=True,
@@ -1181,7 +1178,6 @@ def checkout(options, git_slns, specs, revisions, step_text, shallow):
     got_revisions = { 'got_revision': 'BOT_UPDATE_NO_REV_FOUND' }
     #raise Exception('No got_revision(s) found in gclient output')
 
-  if options.output_json:
   # Tell recipes information such as root, got_revision, etc.
   emit_json(options.output_json,
             did_run=True,