Enhance error handling for tasks

[cherylking]

Fixes #850

The following logic has been added to help deal with a missing server.xml file in a running Liberty server.

CreateTask

• change the upToDateWhen check to include the existence of the server.xml file
• change the create logic to handle the server directory existing but the server.xml file not existing by copying over the defaultServer template server.xml file (this file will get overwritten by the project provided server.xml file if one exists)

RunTask

• change the shutdown hook logic to handle the server directory existing but the server.xml file not existing by copying over the defaultServer template server.xml file (this file will get overwritten by the project provided server.xml file if one exists)

StatusTask

• check for existence of server.xml before issuing the server status command

StopTask

• change the stop logic to handle the server directory existing but the server.xml file not existing by copying over the defaultServer template server.xml file
• after the server stops, delete the server.xml file that was copied over (this will allow the CreateTask to detect that it is not upToDate and replace with the appropriate server.xml file on a subsequent task)