Still getting an error message when attempting to apply Nginx.NG

ExecStartPre has nginx -t to test the Nginx config before starting
the service initially but ExecReload will just issue an Nginx reload
without testing the config first. If the config ends up being bad
this takes Nginx down. Perform a config test before reloading and if
that fails leave Nginx running on the previous config in RAM.

default value if dhparam isn't defined in the pillar.

Improvement - Disable reload of nginx when enabled=False (previously the nginx was always reloaded if settings.config != None; even with enabled=False)

In order to improve security and ease of use, added creation/generation
of dhparam file.

Removed comment after testing that this change works with xenial

Fixes #70

Build NGINX from source with nginx.ng state with support for passing
compile time flags necessary for installing modules such as more headers
by the openresty project.