webtry: Switch from Go's log package to golang/glog.

BUG=skia:2980
TEST=go get -d && go build webtry.go
R=jcgregorio@google.com

Review URL: https://codereview.chromium.org/655323002
webtry: Forgot onr log.Fatal.

Update it to use glog variant.

BUG=skia:2980
TEST=go build webtry.go
TBR=jcgregorio@google.com

Review URL: https://codereview.chromium.org/659813003