feat(protractor): add support for promises in configs

Change driverProviders/hosted to resolve promise values
in configuration to allow async jobs in setup.  Primarily,
this would be for a network call to acquire a selenium host
or to start a proxy server.
Sounds good - the proxy additions can wait, but `seleniumAddress` is a must-have. We'll update the PR next week as my colleague (Sam) is out for the week. Thanks!