The Openroaming help button should show only when the getHelpUriString() value is not null, and need to handle the click event in Settings APP.
Bug: 146669261
Test: Adjust unit test cases:
1. make RunSettingsRoboTests ROBOTEST_FILTER=WifiEntryPreferenceTest
2. make RunSettingsRoboTests ROBOTEST_FILTER=WifiSettings2Test
Change-Id: I27a717c3014b01cc464908bac56f64bd08aa5da3