Replace deprecated ioutil

Package `io/ioutil` was deprecated in golang 1.16, preventing podman from
building under Fedora 37.  Fortunately, functionality identical
replacements are provided by the packages `io` and `os`.  Replace all
usage of all `io/ioutil` symbols with appropriate substitutions
according to the golang docs.

Signed-off-by: Chris Evich <cevich@redhat.com>