Restructure drivers module structure to separate base drivers from device-family specific drivers

As a deployer, I would like to have better control over what device-specific software is loaded in ONOS, so that I can run only the software required for support of devices in my deployment.

Implementation Notes:

• Separate the default drivers that implement the DefaultDriverProviderService into its own onos-default-drivers bundle & app
  • delivers the Pipeliner and OpenFlowSwitchDriver behaviours for generic devices
• Separate drivers that support specific device families into their own modules
  • can include overrides for Pipeliner and OpenFlowSwitchDriver

See https://docs.google.com/a/onlab.us/presentation/d/1LDItacqdWbXESbCAuQhC9QLtTlt6wR82QTDYmAw-xbk/edit?usp=sharing