Custom CLI command line argument passing for the preprovision_olt command

For some device adapters, the ability to pass down additional custom arguments for the preprovisioning_olt command is required. These additional arguments can be used for device specific items such as connection credentials (username, passwords, certificates, ...)

A discussion on this topic is available on the VOLTHA Discuss google group at: https://groups.google.com/a/opencord.org/forum/#!topic/voltha-discuss/5W8DaChQA1s