Android: Get SSL root certificates from TrustManager

On Android, when not using Ministro, we cannot read certificates
from the file system, so we have to get them through Java APIs instead.

Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
(cherry picked from commit 591584d9a940d374e20a62573d71054e0081c6ac)

Task-Number: QTBUG-32508
Change-Id: Ia157e28bc3b2c141e3444d628e7a7c59eca39db0
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>