OpenSSLEngine: do not try to load ENGINE for BoringSSL

Since BoringSSL doesn't use ENGINE instances, we should not fail when
the native code returns the equivalent of a NULL instance. This change
propagates the knowledge of whether we're using BoringSSL or OpenSSL up
to the Java layer.

Change-Id: Ib8c2224a909564ae6f0c6d5984020c44517f6c29
3 files changed