Clean up Kythe language server flag handling.
Clean up Kythe language server flag handling.

Summary:
Consolidate the two flags --host and --port down to a single server address.
Pull out some of the log file setup into a more readable form.

Reviewers: salguarnieri, #core_team

Reviewed By: salguarnieri, #core_team

Subscribers: #core_team

Differential Revision: https://phabricator-dot-kythe-repo.appspot.com/D2171

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