Use buildah commit and bud in podman

Vendor in buildah and use as much of commit and bug as possible for podman
build and commit.

Resolves #586
Signed-off-by: baude <bbaude@redhat.com>

Closes: #681
Approved by: mheon

vendor/github.com/openshift/imagebuilder/strslice/strslice.go

@@ -0,0 +1,30 @@
+package strslice
+
+import "encoding/json"
+
+// StrSlice represents a string or an array of strings.
+// We need to override the json decoder to accept both options.
+type StrSlice []string
+
+// UnmarshalJSON decodes the byte slice whether it's a string or an array of
+// strings. This method is needed to implement json.Unmarshaler.
+func (e *StrSlice) UnmarshalJSON(b []byte) error {
+	if len(b) == 0 {
+		// With no input, we preserve the existing value by returning nil and
+		// leaving the target alone. This allows defining default values for
+		// the type.
+		return nil
+	}
+
+	p := make([]string, 0, 1)
+	if err := json.Unmarshal(b, &p); err != nil {
+		var s string
+		if err := json.Unmarshal(b, &s); err != nil {
+			return err
+		}
+		p = append(p, s)
+	}
+
+	*e = p
+	return nil
+}