Summary: Fix bridge parsing when bridge names are subsets of others

Detail: There are several places in the code that do a
"brctl show | grep bridgeName" or similar, which causes all sorts
of problems when you have for example a cloudVirBr50 and a
cloudVirBr5000. This patch attempts to stop relying on the output
of brctl, instead favoring sysfs and /sys/devices/virtual/net.
It cuts a lot of bash out altogether by using java File. It was
tested in my devcloud-kvm against current 4.0, as well as by the
customer reporting initial bug.

BUG-ID: CLOUDSTACK-938
Fix-For: 4.0.1
Signed-off-by: Marcus Sorensen <marcus@betterservers.com>