installerType 
  Type of the package installer implementation.
Default value is InstallerType.DEFAULT.
When getting/setting the value of this property, the following invariants are maintained:
- When on API level < 21, InstallerType.INTENT_BASED is always returned/set regardless of the current/provided value; 
- When on API level >= 21 and apks contain more than one entry, InstallerType.SESSION_BASED is always returned/set regardless of the current/provided value.