Handle Qual DBs based on default board name.
Handle Qual DBs based on default board name.

All Qual DBs may be existed in the same directory of hardware_Components (overlaid internal git). So, if QUALDB is not specified, first check the existence of DBs matched the board name. Then remove other DBs not belonging to the board.

TEST=build_packages, build_image, image_to_usb

Review URL: http://codereview.chromium.org/3032036

vmware/coreos-scripts,fivethreeo/scripts,trnubo/scripts,zhang0137/scripts,sigma/coreos-scripts,glevand/coreos--scripts,crawford/scripts,endocode/scripts,endocode/scripts,andrejro/coreos--scripts,bcwaldon/coreos-scripts,endocode/scripts,gtank/scripts,smilart/scripts,coreos/scripts,andrejro/coreos--scripts,marineam/coreos-scripts,fivethreeo/scripts,smilart/scripts,trnubo/scripts,gtank/scripts,mischief/scripts,andrejro/coreos--scripts,crawford/scripts,sigma/coreos-scripts,BugRoger/scripts,bcwaldon/coreos-scripts,zhang0137/scripts,fivethreeo/scripts,nicescale/scripts,crawford/scripts,mischief/scripts,sigma/coreos-scripts,smilart/scripts,trnubo/scripts,BugRoger/scripts,mjg59/scripts,mjg59/scripts,nicescale/scripts,gtank/scripts,vmware/coreos-scripts,mjg59/scripts,bcwaldon/coreos-scripts,mischief/scripts,coreos/scripts,nicescale/scripts,marineam/coreos-scripts,glevand/coreos--scripts,BugRoger/scripts,zhang0137/scripts,vmware/coreos-scripts,marineam/coreos-scripts