937d527ac0 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
a1ffd908d7