(NETDEV-29) Enhance netdev NTP api

[shermdog]

This commit enhances the existing ntp_config and ntp_server methods and adds ntp_auth_key per changes in puppetlabs/netdev_stdlib#21

ntp_config

• authenticate
• trusted_key

ntp_server

• key
• maxpoll
• minpoll
• source_interface
• vrf

ntp_auth_key

• key
• algorithm
• mode
• password

[eosplus-jenkins]

Can one of the admins verify this patch?

[shermdog]

@jerearista fixed up.