Remove go cache dir
Remove go cache dir

It saves about 290M.

Change-Id: I603c689be989a603e933970f52510026026c7001
Signed-off-by: Cédric Ollivier <d48310251a4a484d041bc5d09a9ac4d86d20f793@orange.com>

opnfv/functest,opnfv/functest