Fixes bug#1330968  [Config-Policy::Apply Service and Mirror to multi select boxes are not showing place holders]
1. Added placeholder text for inputbox that's shown on checking "Services" checkbox in Create/Edit Policy Dialog
2. Fixed the issue that placeholder text is not shown for Services/Mirror inputboxes initially by specifying the width for these select2 components

Change-Id: Ia7fe1b360dacecc011eeb6301546b943803035d2