Device Identifier for FBSnapshotTestCase

- (NSString *)deviceIdentifier NS_AVAILABLE_IOS(8_0) {
    
    UIScreen *screen = [UIScreen mainScreen];
    
    CGSize size = screen.nativeBounds.size;
    CGFloat scale = screen.nativeScale;
    
    NSString *identifier = [NSString stringWithFormat:@"w_%.00f_h_%.00f", size.width / scale , size.height / scale];
    
    return identifier;
}