veyron/runtimes/google/vtrace: Add capturing via regexps to vtrace.

This CL makes VTrace easier to use.
- Add a flag that specifies a regexp pattern so you can select
  traces by span name or annotation.
- Turn dump_on_shutdown on by default.

Now you can run vtrace with just:
 --veyron.vtrace.collect_regexp=.*

Change-Id: I9b3692aa9871e466aa3f5c0fbeaa4719e843d9e1
8 files changed
tree: c23b60332f257acb1389ab9c895a4e4858f51bd4
  1. lib/
  2. profiles/
  3. runtimes/
  4. security/
  5. services/
  6. tools/