Possible Security Issue in org/conscrypt/Platform.java

Hi,

It looks like function _OpenSSLKey_ of [Platform.java](https://github.com/google/conscrypt/blob/master/android/src/main/java/org/conscrypt/Platform.java) exposes private key in log. The code can be found in both 2.5.x version and master branch.

`
if (opensslKey == null) {
// Bail when detecting OEM "enhancement".
Log.e(TAG, "Could not getOpenSSLKey on instance: " + javaKey.toString());
return null;
}
`

Thanks.