[r=andreserl][bug=][author=mpontillo] Improve switch hardware discovery and tagging.
* Add detection for Broadcom Trident II based switch ASICs.
* Add detection for Broadcom Tomahawk based switch ASICs.
* Add a tag for the specific switch ASIC that was detected.
* Use existing modaliases instead of an extra commissioning script
calling dmidecode on the commissioning node.
* Remove oboslete bash script to detect switch model.
* Add 'switch' tag if we detect a known switch ASIC.
* Add model/vendor tags if we detect a known switch.
* Add serial console kernel parameters if we can detect a known
switch model.