Cover image cannot be added without unfiltered_html capability #2539
Description
When adding a Cover Image block to a post, the resulting <section> element is supposed to have a style attribute with a background image:
<section class="wp-block-cover-image has-background-dim" style="background-image:url(https://melchoycetestingpressable.mystagingwebsite.com/wp-content/uploads/2017/02/cropped-pexels-photo-297755.jpeg)">
<h2>This is a cover block</h2>
</section>
However, testing Gutenberg 0.9.0 as an admin user on a Multisite network, the style attribute is stripped, resulting in a section with no background image:
<section class="wp-block-cover-image has-background-dim">
<h2>This is a cover block</h2>
</section>
At a glance, it's because in Multisite regular admins don't have the unfiltered_html capability, only super admins do.