test/int/spec.bats: simplify setup/teardown
test/int/spec.bats: simplify setup/teardown

1. cd is useless as all the paths are absolute
2. run is redundant, does not make sense to use it
3. use mkdir -p to save a line of code

This also eliminates shellcheck warnings like this one:

> In spec.bats line 8:
>   cd "$INTEGRATION_ROOT"
>   ^--------------------^ SC2164: Use 'cd ... || exit' or 'cd ... || return' in case cd fails.

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

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