[KV] Refactor logs

Unify formatting. Start w/ upper case, using ',' instead of ';', '-'.

Test: atest KeyValueBackupTask
Test: 1. adb shell bmgr backupnow com.google.android.apps.backupapp
      2. Verify logs
Test: atest CtsBackupTestCases
Test: atest CtsBackupHostTestCases
Test: atest GtsBackupTestCases
Test: atest GtsBackupHostTestCases

Change-Id: I171110f69e66d0311cbf030b210600ddf1ad5656