libct/nsenter: test: improve newPipe
libct/nsenter: test: improve newPipe

1. Make sure we close all file descriptors at the end of the test.

2. Make sure we close child fds after the start.

3. Use newPipe for logs as well, for simplicity and uniformity.

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

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