CI: add shellcheck of bats files
CI: add shellcheck of bats files

Currently all the shellcheck warnings are fixed, and we'd like it to
stay thay way. So, add shellcheck call to validate target in Makefile,
which is run on Travis CI.

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

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