Change ImageBackground to work with percentage image sizes
Change ImageBackground to work with percentage image sizes

Summary: ImageBackground assigned its Image the same `width` and `height` styles as itself. This became an issue for ImageBackground instances that were assigned (non 100%) percentage size values. For example, if the `width` and/or `height` of the ImageBackground was set to be 50%, it would be half the size of the current component it is in (as intended), but the Image would be 50% of the ImageBackground, which is only 25% the size of the ImageBackground's parent component.

Reviewed By: shergin

Differential Revision: D9307123

fbshipit-source-id: cec3802d30b72c44f66dd3a53693ebd669cc8db4

facebook/react-native,hammerandchisel/react-native,facebook/react-native,arthuralee/react-native,myntra/react-native,javache/react-native,javache/react-native,myntra/react-native,exponentjs/react-native,janicduplessis/react-native,javache/react-native,myntra/react-native,myntra/react-native,exponent/react-native,exponentjs/react-native,hoangpham95/react-native,pandiaraj44/react-native,hoangpham95/react-native,javache/react-native,arthuralee/react-native,arthuralee/react-native,janicduplessis/react-native,janicduplessis/react-native,hoangpham95/react-native,myntra/react-native,exponentjs/react-native,facebook/react-native,hoangpham95/react-native,hammerandchisel/react-native,exponent/react-native,janicduplessis/react-native,janicduplessis/react-native,facebook/react-native,pandiaraj44/react-native,javache/react-native,hoangpham95/react-native,pandiaraj44/react-native,exponent/react-native,hammerandchisel/react-native,pandiaraj44/react-native,myntra/react-native,exponent/react-native,facebook/react-native,facebook/react-native,exponent/react-native,javache/react-native,facebook/react-native,javache/react-native,exponentjs/react-native,facebook/react-native,exponent/react-native,exponentjs/react-native,exponentjs/react-native,janicduplessis/react-native,pandiaraj44/react-native,hoangpham95/react-native,arthuralee/react-native,hoangpham95/react-native,hammerandchisel/react-native,janicduplessis/react-native,pandiaraj44/react-native,hammerandchisel/react-native,exponent/react-native,hammerandchisel/react-native,myntra/react-native,hammerandchisel/react-native,hoangpham95/react-native,pandiaraj44/react-native,exponent/react-native,exponentjs/react-native,javache/react-native,myntra/react-native,myntra/react-native,janicduplessis/react-native,arthuralee/react-native,javache/react-native,exponentjs/react-native,facebook/react-native,hammerandchisel/react-native,pandiaraj44/react-native