libct: fixStdioPermissions: minor refactoring
libct: fixStdioPermissions: minor refactoring

Use os/file Chown method instead of bare unix.Fchown as it already have
access to underlying fd, and produces nice-looking errors. This allows
us to remove our error wrapping and some linter annotations.

We still use unix.Fstat since os.Stat access to os-specific fields
like uid/gid is not very straightforward. The only change here is to use
file name (rather than fd) in the error text.

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

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