Allow client consumers like traefik to compile on illumos

Signed-off-by: Till Wegmüller <toasterson@gmail.com>

client/client_unix.go

@@ -1,4 +1,4 @@
-// +build linux freebsd openbsd darwin
+// +build linux freebsd openbsd darwin solaris illumos
 
 package client // import "github.com/docker/docker/client"