veyron/runtimes/google/ipc: Refresh server discharges before they expire.

This change does the following:
(1) The DischargeClient will re-fetch expired discharges if it detects
    they are expired as it is looking for discharges in the cache.
(2) The VC sends re-fetched discharges from the server side to the client
    side when it detects a discharge is expired.

Change-Id: I52279088c1caa824d969cd112b55a692a1af669e
7 files changed
tree: 7c24235013217fc82e56ffdef19406bcc7cfd043
  1. lib/
  2. profiles/
  3. runtimes/
  4. security/
  5. services/
  6. tools/