added single service and multiple service tests

Added some tests to the bakery for single service and multiple service scenarios
How about making a helper function:

    func newService(c *gc.C, location string, locator bakery.PublicKeyLocatorMap) *bakery.Service {
    	keyPair, err := bakery.GenerateKey()
    	c.Assert(err, gc.IsNil)

    	svc, err := bakery.NewService(bakery.NewServiceParams{
    		Location: location,
    		Key:      keyPair,
    		Locator:  s.locator,
    	})
    	c.Assert(err, gc.IsNil)
    	if locator != nil {
    		locator[location] = &keyPair.Public
    	}
    	return svc
    }
    
Then setUpFig6Services becomes somewhat redundant.
You can just do this directly in the tests:
     locator := make(bakery.PublicKeyLocatorMap)
     as := newService(c, "loc-as", locator)
     ts := newService(c, "loc-ts", locator)
     fs := newService(c, "loc-fs", locator)

which probably makes the tests a little bit more obvious than setUpFig6Services, and opens the door to more similar tests too.
I wondered about putting the locator into ServiceSuite and making newService a method on ServiceSuite that adds the service location to the suite. YMMV about that.