Could not download and install iOS 7.1 Simulator. Failed to mount  file:///Users/myusername/Library/Caches/com.apple.dt.Xcode/Downloads/Xcode.SDK.iPhoneSimulator.7.1-7.1.dmg at file:///var/folders/f8/4wmmmwj17_96v9jp7h1f4gqc0000gn/T/attached-image-85355a6e6ed97fd1899b8ef3a6052181e745b5fb/: image not recognized