This factory determines what Engine should be used with the supplied httpClient
If no Httpclient is specified we use the new config style engine if allowed
In case of an InputStream or Reader and a invocation that returns no Response object, we need to make
sure the GC does not close the returned InputStream or Reader
When the user is not using a TrustManager (see disableTrustManager) and
does not define an SSLContext object but they want all defined trustStores
to use the TrustSelfSignedCertificates trust strategy set this value to true.