Fix some "no such provider" initialisation errors in tests

Caused by: java.security.NoSuchProviderException: no such provider: BC	at sun.security.jca.GetInstance.getService(GetInstance.java:83)	at sun.security.jca.GetInstance.getInstance(GetInstance.java:206)	at java.security.Signature.getInstance(Signature.java:355)	at org.bouncycastle.jcajce.NamedJcaJceHelper.createSignature(NamedJcaJceHelper.java:95)