Fix typo npt:ntpd_conf -> ntp:ntpd_conf
Fix ntpd_conf ID clash

If both ntp:ntp_conf and ntp:ntpd_conf pillar values are set and one
applies ntp.server then ntpd_conf ID will be defined leading to clash.

This was probably a copy & paste error.
Simplify optional config management

If either ntp:ntp_conf or ntp:ntpd_conf are missing the whole
file.managed section would have been excluded by Jinja.

So there was no point of falling back to defaults inside those sections.

Also using variables makes the state less error prone.
Merge pull request #8 from opennode-salt-formulas/typos

Typos and config files management fixes