tests: add integration tests for dap build

This adds integration tests for the `dap build` command to test various
behavior associated with the command. We start the build and the
integration test acts as a dap client to send requests and check that
the output is what we expect.

Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>

tests/integration_test.go

@@ -34,6 +34,7 @@ func TestIntegration(t *testing.T) {
 	tests = append(tests, dialstdioTests...)
 	tests = append(tests, composeTests...)
 	tests = append(tests, diskusageTests...)
+	tests = append(tests, dapBuildTests...)
 	testIntegration(t, tests...)
 }