Installd: don't generate app image with empty reference profile

Use app images only if we are compiling profile-guided and
reference profile not empty.

Fixed test logic to use a non-empty dm_file so that the profile is actually opened by dexopt.cpp.

Test: 1.adb install old_version.apk
      2.open and use app for a while and make sure the reference profile generated
      3.adb install new_version.apk
      4.check if app image file exists?

Bug: 270427379
Change-Id: If143605e0f5541fcffd63aa52a257834d2448383