No panic when could not find glog flag.

[kuba--]

Signed-off-by: kuba-- kuba@sourced.tech

What we have in go/vt/logutil/level.go is bad.
In file go/vt/log/log.go it says:

You can modify this file to hook up a different logging library instead of glog.

But actually level.go is looking for glog flags (stderrthreshold) and panics (if not found)!

This PR (at least) removes panic from init function.

[kuba--]

• why SHARD4 is failing with ./test.go:880: d.Round undefined (type time.Duration has no field or method Round)?
  It's totally not related to PR.

[sougou]

Not sure what happened. But the retry succeeded. I plan on reviewing all pending PRs by EOW.