tests/int: add rootless + host pidns test case
tests/int: add rootless + host pidns test case

For the fix, see previous commit. Without the fix, this test case fails:

> container_linux.go:380: starting container process caused:
> process_linux.go:545: container init caused: readonly path /proc/bus:
> operation not permitted

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

dqminh/runc,opencontainers/runc,kolyshkin/runc,kolyshkin/runc,rhatdan/runc,opencontainers/runc,dqminh/runc,kolyshkin/runc,rhatdan/runc,opencontainers/runc,dqminh/runc,opencontainers/runc,rhatdan/runc,kolyshkin/runc,dqminh/runc,rhatdan/runc