test: clean up tests for traffic director

[igorbernstein2]

• add ability to override the app profile for a test run
• ensure to skip the metrics it test since it uses an ephemeral app profile
• add interceptor to fail any test that overrides the app profile when the app profile is specified
• remove unused method
• remove old user agent test hack

Change-Id: Iee431c1a5b979bef45785d08c41125945c76e6bb

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Fixes #<issue_number_goes_here> ☕️

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