authcli: Handle case when -scopes CLI argument doesn't include email scope.
authcli: Handle case when -scopes CLI argument doesn't include email scope.

In that case we can't report user's email, but it's not big deal.

Useful when caching tokens for PubSub API (used by tsmon, for example):
$ ./authutil login -scopes "https://www.googleapis.com/auth/pubsub"

R=nodir@chromium.org
BUG=

Review-Url: https://codereview.chromium.org/2013613002

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go