Added amazon-fireos platform.
1. Updated CLI readme.md. Added amazon-fireos platform specific changes.
   Still missing AWV SDK URL.
2. Updated check_requirements method to check for awv_interface.jar in framework_path/libs folder.
   This change ensures we build the cordova.jar only if awv_interface.jar exists in the framework_path/libs folder. If the awv_interface.jar is missing, an appropriate error message is displayed along wit
Updated amazon-fireos url to point to github.