Temporarily disable py36
Temporarily disable py36

Build servers haven't been updated yet to support py36.

Change-Id: I6e396f944e7226d682a58c8e74ed136e0b55d2cd
Signed-off-by: Cédric Ollivier <d48310251a4a484d041bc5d09a9ac4d86d20f793@orange.com>

opnfv/functest,opnfv/functest