fa739d4bd7 qa: Add wallet_encryption error tests (MarcoFalke)
Pull request description:
The errors for empty passphrases are the help text of the RPC call, which is not very specific. Replace that with proper RPC errors and test them.
Tree-SHA512: 3137e0f8f2e42a1f8ab1eeb57c99052557725f6f85139ff48c24acc8f3cf4087802de5216f3ce97375b291d21bddb7cd1379a6f280166136a306a0c9663bbd42
Backport of Core PR14813