Update c/image to v4.0.1 and buildah to 1.11.3

This requires updating all import paths throughout, and a matching
buildah update to interoperate.

I can't figure out the reason for go.mod tracking
	github.com/containers/image v3.0.2+incompatible // indirect
((go mod graph) lists it as a direct dependency of libpod, but
(go list -json -m all) lists it as an indirect dependency),
but at least looking at the vendor subdirectory, it doesn't seem
to be actually used in the built binaries.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

vendor/github.com/prometheus/procfs/proc_environ.go

@@ -0,0 +1,43 @@
+// Copyright 2019 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package procfs
+
+import (
+	"io/ioutil"
+	"os"
+	"strings"
+)
+
+// Environ reads process environments from /proc/<pid>/environ
+func (p Proc) Environ() ([]string, error) {
+	environments := make([]string, 0)
+
+	f, err := os.Open(p.path("environ"))
+	if err != nil {
+		return environments, err
+	}
+	defer f.Close()
+
+	data, err := ioutil.ReadAll(f)
+	if err != nil {
+		return environments, err
+	}
+
+	environments = strings.Split(string(data), "\000")
+	if len(environments) > 0 {
+		environments = environments[:len(environments)-1]
+	}
+
+	return environments, nil
+}