Log some actions for changing wifi hotspot config

Log following actions:
- wifi hotspot name changed
- wifi hotspot password changed

Added tests for logging actions in each controller's test.

Bug: 151113705
Test: WifiTetherSSIDPrefereceControllerTest;
WifiTetherPasswordPreferenceControllerTest;
CodeInspectionTest

Change-Id: I84b1cd8449e575a6ee1ad8868e7791dc601e726f