test: improve numerous http tests
Minor refactoring in a number of http tests. I've been going through an auditing the existing http tests to identify which we will need equivalents for on the http2 implementation and spotted a number of cleanups that could be made.
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
commit message follows commit guidelines
Affected core subsystem(s)
tests (http)