Refactor New for E36xx to handle different types of DCPwr instruments

[matthewrankin]

If a single driver is going to handle multiple models, I'll need to implement one or possibly multiple of the following new functions:

1. Have specific new functions for each supported model, such as NewE3631A(inst) instead of New(inst)
2. Have a NewQuery(inst) function that queries the instrument and confirms it is supported.
3. Have a New(inst, model) function that specifies the model of the instrument to create.

In all of these, how do I handle passing in an option to reset the device? Is that always a boolean that is provided? What if I want to specify NewE3631A(inst) and I also want to query the device to ensure it actually that? I could simply mandate that a query is always performed.

[matthewrankin]

Thoughts on the API to create a new DC power supply in the case where one IVI driver supports multiple models, such as handling models with different number of outputs.

type inst ivi.Instrument
type Config struct {
    model string
    queryId bool
    reset bool
}
config := Config{"E3631A", true, false}
dc, err := agilente36xx.New(inst, config)