Revert use of PAX archives

Revert the use of POSIX PAX archive format in TarFileArchive. The
code to capture SELinux file contexts is currently disabled in
master due to the undesirable affects on archive extraction. Since
this is the main reason for using the PAX format revert to
automatic format selection to allow the widest compatibility.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>
Set umask when creating final archive file

The temporary trees used by sos are set up with correct
permissions but tarfile.open() uses the default mode and umask
settings.

Set the umask to deny group and other permissions for the archive
to avoid leaking data to unprivileged users.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>