new_variant: add hashtag for finding uploaded CLs

To make it easier to find CLs that new_variant.py uploaded on behalf
of any user, add a --hashtag option to the repo upload command. We
can search gerrit for all CLs with this hashtag to find all CLs that
new_variant.py uploaded.

BUG=b:167302175
TEST=n/a

Change-Id: I0b022bd6c00b11acb03f3899780102635707d87f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2387595
Reviewed-by: Jack Rosenthal <jrosenth@chromium.org>
Commit-Queue: Paul Fagerburg <pfagerburg@chromium.org>
Tested-by: Paul Fagerburg <pfagerburg@chromium.org>
diff --git a/contrib/variant/new_variant.py b/contrib/variant/new_variant.py
index 0a4ef50..143d87d 100755
--- a/contrib/variant/new_variant.py
+++ b/contrib/variant/new_variant.py
@@ -1237,7 +1237,8 @@
         '--br=' + branch_name,
         '--wip',
         '--verify',
-        '--yes'],
+        '--yes',
+        '--hashtag=new_variant'],
         cwd=cwd)