Allow forced backup deletion

Add --force and --confirm to `ark backup delete` to support forced
backup deletion. This forcibly removes the Ark GC finalizer (if it's
present) from a backup and will orphan any resources associated with the
backup, such as backup tarballs in object storage, persistent volume
snapshots, and restores for the backup.

If a backup has a deletion timestamp, display `Deleting` in `ark backup
describe` and `ark backup get`.

Signed-off-by: Andy Goldstein <andy.goldstein@gmail.com>

pkg/util/stringslice/stringslice.go

@@ -0,0 +1,44 @@
+/*
+Copyright 2018 the Heptio Ark contributors.
+
+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 stringslice
+
+// Has returns true if the `items` slice contains the
+// value `val`, or false otherwise.
+func Has(items []string, val string) bool {
+	for _, itm := range items {
+		if itm == val {
+			return true
+		}
+	}
+
+	return false
+}
+
+// Except returns a new string slice that contains all of the entries
+// from `items` except `val`.
+func Except(items []string, val string) []string {
+	// Default the capacity the len(items) instead of len(items)-1 in case items does not contain val.
+	newItems := make([]string, 0, len(items))
+
+	for _, itm := range items {
+		if itm != val {
+			newItems = append(newItems, itm)
+		}
+	}
+
+	return newItems
+}

pkg/util/stringslice/stringslice_test.go

@@ -0,0 +1,46 @@
+/*
+Copyright 2018 the Heptio Ark contributors.
+
+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 stringslice
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestHas(t *testing.T) {
+	items := []string{}
+	assert.False(t, Has(items, "a"))
+
+	items = []string{"a", "b", "c"}
+	assert.True(t, Has(items, "a"))
+	assert.True(t, Has(items, "b"))
+	assert.True(t, Has(items, "c"))
+	assert.False(t, Has(items, "d"))
+}
+
+func TestExcept(t *testing.T) {
+	items := []string{}
+	except := Except(items, "asdf")
+	assert.Len(t, except, 0)
+
+	items = []string{"a", "b", "c"}
+	assert.Equal(t, []string{"b", "c"}, Except(items, "a"))
+	assert.Equal(t, []string{"a", "c"}, Except(items, "b"))
+	assert.Equal(t, []string{"a", "b"}, Except(items, "c"))
+	assert.Equal(t, []string{"a", "b", "c"}, Except(items, "d"))
+}