Single app package support including service app

Single app package support including service app

To run Tizen TCT packages, single-app packages having only service apps
must be able to be installed. This commit enables installing app packages
having only service apps.
  - Removed mandatory ui-application app checking routine.
  - Added a routine checking the existance of at least 1 ui or service app.
  - Additional code for <service-application> attributes in
    step_generate_xml.cc.

Change-Id: Iaac04f6fb20055fe06ca6b3a67294c9354695ec0
Signed-off-by: Youmin Ha <youmin.ha@samsung.com>