Adding system interaction functions

For now we can run a service commad

system.go

@@ -0,0 +1,41 @@
+package owrt
+
+import (
+	"fmt"
+)
+
+// SysAction is the result of an UCI action output and return code
+type SysAction struct {
+	*CommandResult
+	Command string
+}
+
+// System "Object", an inteface with openwrt system
+type System struct {
+	exec Executor
+}
+
+// NewSystem return an OpenWRT System instance to interact with UCI
+func NewSystem() *System {
+	exec := &localExecutor{}
+	return &System{exec}
+}
+
+// NewSystemWithExecutor returns a System Instance an gives you the ability to provide
+// a different command executor than the default one.
+func NewSystemWithExecutor(exec Executor) *System {
+	return &System{exec}
+}
+
+// sysRun, private method to run the UCI command
+func (s *System) sysRun(param ...string) *SysAction {
+	cmd := param[0]
+	res := s.exec.Run(cmd, param...)
+	return &SysAction{res, fmt.Sprintf("%s %s", cmd, param)}
+}
+
+// Service implementation of "service" command
+func (s *System) Service(name string, action string) *SysAction {
+	cmd := fmt.Sprintf("/etc/init.d/%s ", name)
+	return s.sysRun(cmd, action)
+}