Consolidate adb helper methods into single class.

This makes them easier to invoke and prevents confusion by separating them
normal from production and test code.

Test
$ adb shell am instrument -e method addTestAccount -e accountName fooAccount\
$  -w com.android.contacts.tests/com.android.contacts.RunMethodInstrumentation

Change-Id: I443681b4b8ed526c390e593540c5e2910d97f6b4