ADT: fixes to make Proguard work under Windows.

ADT: fixes to make Proguard work under Windows.

- the proguard.bat can only pass 9 args, but we have 15+, so
  we'll use a temporary proguard config file for Windows.

- PROGUARD_HOME needs to be defined properly since the default
  proguard.bat cannot infer it properly. We need other fixes
  to that batch file so eventually we're not going to ship the
  default one and we can fix the .bat file, but properly defining
  this env var is probably a good idea anyway.

Change-Id: Id007d5504a5e05d1c4b5a0728e96e0d677978ef4