refactor: wait for sb to load before taking snapshot

Author: matthewgallo

.percy.yml

@@ -8,6 +8,11 @@ snapshot:
 discovery:
   network_idle_timeout: 750
 storybook:
+  waitForTimeout: 1000
+  # waits for data-carbon-theme attribute to exist before taking snapshot
+  # if storybook is still loading, percy could take a snapshot of the storybook
+  # loading spinner and cause flaky tests
+  waitForSelector: [data-carbon-theme]
   include: ['/IBM Products/']
   exclude: [
       '/Internal/',