Update task states tests

*Updated task states tests
-Updated tests due to behavior, fixture and config changes
-Added import_task_states_failure test
-Added export_task_states_success test
-Added export_task_states_failure
-Updated variable names for clarity
-Moved messages to constants
-Updated task transition validation

Change-Id: I7da4dd04225911d74b00b041d439f0e32839ab2d
Merge "Update task states tests"