Identify in logs launch of voice search from key events

Clearly identify in the logs when AudioService starts one of
 the following two intents in response to long-press on
 the KEYCODE_HEADSETHOOK key: ACTION_WEB_SEARCH and
 ACTION_VOICE_SEARCH_HANDS_FREE.

Bug 8095981

Change-Id: I14ca99533dfb011cdc530c0bafd8104ff2436c7d