Java: RPC performance improvements for Java

We were extremely inefficient handling Java <-> Go conversions on
a perf-critical part, in particular:

  - VOM-copying blessings (thrice) for blessings conversions,
  - VOM-copying caveats as FixedLengt<Byte> arrays, which is
    inefficient,
  - CaveatValidation in Java is expensive as it requires caveat
    to be converted.

The fixes reduce the RPC RTT time from 280ms to around 70ms.

MultiPart: 1/2
Change-Id: I541b9883d50db90f7e68aa1b9e23aa429aaffb72
5 files changed