Keystore 2.0: Add error string to service specific exceptions.

This patch adds detailed error messages to the service specific
exceptions. The error messages are formated anyhow::Errors, the same
that already get logged to logcat. Returning them to the client, allows
them to be included in java stack traces which will lead to easier
diagnosis of bugreports.

Test: N/A
Bug: 197890905
Change-Id: Ie6178292650327a1382b04f478ed5fa9e5fd7feb
4 files changed