When we detaching subnet from one dhcp edge and deploying a new dhcp edge
for the subnet, there is a chance that we would use a duplicate name for
the new dhcp edge and it would lead to duplicate name error at the
backend. Since the edge name is just a tag that we can easily read and
it would not be used in plugin, the patch fixed the problem by using a
randomly unique edge name.
Change-Id: Ia764ec8c7b54e78ed36f827df4e3025d6e309062
Fixes-bug: #1508633
0dcb113c36