container.conf: support attributed string slices

All `[]string`s in containers.conf have now been migrated to attributed
string slices which require some adjustments in Buildah and Podman.

[NO NEW TESTS NEEDED]

Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

vendor/github.com/containers/common/internal/attributedstring/slice.go

@@ -23,6 +23,11 @@ type Slice struct { // A "mixed-type array" in TOML.
 	}
 }
 
+// NewSlice creates a new slice with the specified values.
+func NewSlice(values []string) Slice {
+	return Slice{Values: values}
+}
+
 // Get returns the Slice values or an empty string slice.
 func (a *Slice) Get() []string {
 	if a.Values == nil {
@@ -31,6 +36,11 @@ func (a *Slice) Get() []string {
 	return a.Values
 }
 
+// Set overrides the values of the Slice.
+func (a *Slice) Set(values []string) {
+	a.Values = values
+}
+
 // UnmarshalTOML is the custom unmarshal method for Slice.
 func (a *Slice) UnmarshalTOML(data interface{}) error {
 	iFaceSlice, ok := data.([]interface{})