1. Fixed a case in which the onPrintCompleted callback may not be invoked.
2. Added string resulrces for the different error messages for failed
printing in OnPrintCompletedCallback
3. Fixed the string comments for the MediaSize constants.
4. Added APIs to create certain print attributes by passing in a
string label instead of resource and package name since in some cases
a print service may be getting already internationalized lables
or it may not know all possible values.
5. Fixed a crash in PrintJobConfigActivity if there is no input or
output tray.
Change-Id: Ie877b7dc669051606394aa290e6d2b979a42db4c
17b7f6e6d4