Makefile: add -mod=vendor to go test
Makefile: add -mod=vendor to go test

Otherwise, in case go < 1.14 is used, all the go deps are downloaded
instead of using vendor subdir.

Signed-off-by: Kir Kolyshkin <3a017b8ddb3f9cf3e4a59978b004111bdeb97f08@gmail.com>

estesp/runc,rhatdan/runc,opencontainers/runc,dqminh/runc,mikebrow/runc,dqminh/runc,opencontainers/runc,mikebrow/runc,opencontainers/runc,dqminh/runc,estesp/runc,mikebrow/runc,rhatdan/runc,opencontainers/runc,rhatdan/runc,kolyshkin/runc,xiaochenshen/runc,kolyshkin/runc,xiaochenshen/runc,xiaochenshen/runc,dqminh/runc,kolyshkin/runc,rhatdan/runc,estesp/runc,kolyshkin/runc