Remove unnecessary wrapper for 5 compute APIs

There are 5 APIs in compute layer:
check_instance_shared_storage
change_instance_metadata
add_fixed_ip_to_instance
remove_fixed_ip_from_instance
reset_network
has unnecessary wrapper, this patch removed them

reverts_task_state is a wrapper to restore instance task state
when some thing wrong in executing the task,
change_instance_metadata, add_fixed_ip_to_instance
remove_fixed_ip_from_instance, reset_network doesn't change the state,
so no need to wrap it

wrap_instance_fault is a wrapper to catch the exception related to
instances, check_instance_shared_storage is not related to it

Change-Id: I2c4779c01854c2c8bac40e7379ad2fc4d0a7478a
Merge "Remove unnecessary wrapper for 5 compute APIs"