tests: fix some http/2 tests for older versions of nghttpx #6139
Tests 358 and 359 were failing for me before this change on a system
nghttpx has --server-name which would be a better choice to make a uniform server name however it's not available in some older versions that are still supported.
- Add regex that strips http/2 server header name to those http/2 tests that don't already have it. - Improve that regex in all http/2 tests. Tests 358 and 359 were failing for me before this change on a system that uses an older version of nghttpx which includes its version number in the server header. Closes #xxxx