AI 143885: am: CL 143883 am: CL 143881 AVD #1703143: delete AVDs not loaded correctly.

  This covers the case where an AVD has an invalid target
  or is missing its AVD folder or the config.ini in it.
  Made some cosmetic cleanup too.
  Original author: raphael
  Merged from: //branches/cupcake/...
  Original author: android-build
  Merged from: //branches/donutburger/...

Automated import of CL 143885