make name optional with custom DP's

I noticed that in the jss-autopkg-addon [README.md](https://github.com/sheagcraig/jss-autopkg-addon/blob/JDS-update/README.md) for the JDS-update branch it indicated that the "name" key is optional, but it was raising if left unspecified in the preference.

I wasn't sure if you wanted to set an alternate default value like "JSS_DP_" to protect against mount_point clashes with casper admin, if so let me know and I'd be happy to update this PR.

Thanks,
Eldon