Merge pull request dotnet/corefx#34345 from geoffkizer/genericloopbackserver

Add GenericLoopbackServer for HttpClient testing

Commit migrated from https://github.com/dotnet/corefx/commit/3de6ad8c1233ccf9c781d42a0cdb88b0aeb24cb7

diff --cc src/libraries/System.Net.Http/tests/FunctionalTests/PlatformHandlerTest.cs
Simple merge

diff --cc src/libraries/System.Net.Http/tests/FunctionalTests/SocketsHttpHandlerTest.cs
Simple merge

diff --cc src/libraries/System.Net.Http/tests/FunctionalTests/System.Net.Http.Functional.Tests.csproj
Simple merge