=htc #16488 add missing assertions in tests

 - replaced pure `===` by `shouldEqual`
 - fixed the backport of spray/spray#927 in ae8c47acc170907ee9c8dfbcb946b400035f6877
 - fixed HttpHeaderParserSpec
Merge pull request #16489 from spray/w/16488-fix-http-tests

=htc #16488 add missing assertions in tests