http: throw an error for unexpected agent values
Checklist
-
make -j8 test
(UNIX), orvcbuild test nosign
(Windows) passes -
tests and/or benchmarks are included -
commit message follows commit guidelines
Affected core subsystem(s)
http, test
Description of change
As per #9069 (closed) unexpected things can happen when supplying an unexpected value to agent. Beings as the docs clearly state the expected values, this throws an error on an unexpected value.