Add build flag to exec test.

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jess@docker.com> (github: jfrazelle)

integration-cli/docker_api_exec_test.go

@@ -1,3 +1,5 @@
+// +build !test_no_exec
+
 package main
 
 import (

integration-cli/docker_cli_exec_test.go

@@ -1,3 +1,5 @@
+// +build !test_no_exec
+
 package main
 
 import (