Changes

Fix Bug 2208 KeyError while checking SDN assists requirement
VIM config is optional so code is fixed by checking the existence of VIM
config.
Change-Id: I1aca37cf169a766219630c90968df9d729ffd621 Signed-off-by:
Gulsum Atici <gulsum.atici@canonical.com>
(cherry picked from commit 0b430f6b3690b78474aca98d2112f20a9f56c8a4)