Write salt config to a custom "watchmaker" location

[lorengordon]

Right now we are writing to the default salt config location. This means anyone using salt themselves needs to be aware of what watchmaker does to salt's config and may need to work around the watchmaker configuration in some way.

Salt supports specifying a config directory at runtime, with -c. We can write the watchmaker salt config to a custom location and use this parameter when calling salt. This will avoid stepping on anyone's feet, should they be using salt themselves.

[lorengordon]

When implemented, this should make #402 OBE