Free VC Skewify Row plugin allows you to make Visual Composer rows with skewed top and bottom border.
VC Skewify Row WordPress Plugin Features
It’s very simple to use. Just insert Skewify element into your VC Row and watch the magic! It uses HTML clip-path for cutting out triangles. It has fallback for IE, which requires one sibling row to have solid color background (or you can just turn it off for IE).