Correctly set search string when entering search

Changes
1) When entering search mode, explicitly clear the
 search query
2) Make sure that the cursor starts after the text
 that is programmatically inserted via setQueryText().

Manual tests:
-Type into search bar. Exit app. Resume app.
 Open search bar again. Search bar should be empty.
-Type into search bar. Rotate app. Search bar shouldn't
 be empty.
-Type into search bar. Close search. Open search.
 The search view should be empty.
-execute "$ adb shell input keyboard text abcd". In KK
 the search view will show "dabc". Now this shows "abcd".
-Place cursor in middle of a search term. Enter new text
 using the soft keyboard or use adb shell to enter new text.
 In both cases the new text appears after the cursor
 position.

Bug: 18410365
Change-Id: I7ce260913e3c8e7448678bd2178859fb9c9270ab