Exec errors will be shortened if they exceed max  nats message size

- Exec errors include stdout & stderr, which can be arbitrarily long.
  The stdout & stderr are now each shortened to the last 100 lines if
  they collectively exceed 1MB during NATS message serialization.
- This is a workaround for large package compilation output resulting in
  a NATS message length exceeded error.

[#72630870]

Signed-off-by: dmitriy kalinin <dmitriy@pivotallabs.com>