Attach apk_name as a suffix for the temporary files

With this change the name of the signed and unsigned APK will be something like 'tmpadrbpp9f/tmpvl0lf2kr/tmpknja6mca_MyApk.apk' instead of 'tmpadrbpp9f/tmpvl0lf2kr/tmpknja6mca'.

The motivation for this change is a better logging and transparency what is being signed in the underlying client.

Change-Id: I32b0e93d5859ca3fb712e426705f16d329d71f0e