Startup check on sample interval and euid
Startup check on sample interval and euid

- If we aren't running as root, bail out immediately.
- Set up a static "too low" threshold for sample interval.
- Check to make sure that we are able to keep up with our requested sample interval.
  If not, add in a magic 100ms of time to try to recover. This is awkward, but seems to help.
  Fixes #4

uber-common/cpustat