Vendor in latest projectatomic/buildah

Adds --rm and --force-rm to podman build.

Signed-off-by: umohnani8 <umohnani@redhat.com>

Closes: #945
Approved by: rhatdan

vendor/github.com/projectatomic/buildah/util/util.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"io"
 	"net/url"
+	"os"
 	"path"
 	"strings"
 
@@ -233,3 +234,12 @@ func WriteError(w io.Writer, err error, lastError error) error {
 	}
 	return err
 }
+
+// Runtime is the default command to use to run the container.
+func Runtime() string {
+	runtime := os.Getenv("BUILDAH_RUNTIME")
+	if runtime != "" {
+		return runtime
+	}
+	return DefaultRuntime
+}