Install open ssl jar into Gerrit site for bouncycastle crypto provider

937d527ac0e4ee685fccb60ae604406a6638daec upgraded bouncy castle to 1.49.

The old JAR artifact was renamed and split to number of files. For Gerrit
two libraries must be downloaded and be available under `$gerrit_site/lib`:

* bcprov-jdk15on-149.jar
* bcpkix-jdk15on-149.jar

Update download logic to support a basic concept of required dependencies,
ensuring BC provider is downloaded if the SSL library is installed by init.

Change-Id: I60092ebe136f78a5649fe8512737275f50195a34