Run nghttpx integration test with cmake build. Autotools build erases
artifacts for packaging tests, so we cannot run nghttpx integration
test with autotools build at the moment.
Relay on go modules to download dependencies.
Older automake (travis, *cough*) do not support the
AM_EXTRA_RECURSIVE_TARGETS option, this results in invoking "it-local"
directly in the travis script which relies on an implementation detail.
Since the "it" target is only used by the integration-tests directory,
just avoid the recursive targets. The README.rst suggests to enter the
integration-tests directory anyway.
`go test` requires both config.go and the test files in the same
directory. For out-of-tree builds, config.go is normally not placed next
to the source files, so copy the tests to the build directory as a
workaround.
