Do not quit the service handler looper in WifiScanner

The handler is created WifiFrameworkInitializer as unique and static
instance. If the loop is quit and WifiScanner service is restarted, it will throw
java.lang.NullPointerException at Handler.<init>.

Bug: 183918800
Test: atest WifiScanner.testWifiScannerConcurrentServiceStart
Change-Id: I58853542448005c027ca011e51f99bdb029e757a
Merged-In: I58853542448005c027ca011e51f99bdb029e757a
3 files changed