Add cap-add and cap-drop to build man page

Signed-off-by: TomSweeneyRedHat <tsweeney@redhat.com>

Closes: #968
Approved by: mheon

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

@@ -0,0 +1,39 @@
+package bind
+
+import (
+	"github.com/opencontainers/runtime-spec/specs-go"
+	"github.com/projectatomic/buildah/util"
+)
+
+const (
+	// NoBindOption is an option which, if present in a Mount structure's
+	// options list, will cause SetupIntermediateMountNamespace to not
+	// redirect it through a bind mount.
+	NoBindOption = "nobuildahbind"
+)
+
+func stripNoBindOption(spec *specs.Spec) {
+	for i := range spec.Mounts {
+		if util.StringInSlice(NoBindOption, spec.Mounts[i].Options) {
+			prunedOptions := make([]string, 0, len(spec.Mounts[i].Options))
+			for _, option := range spec.Mounts[i].Options {
+				if option != NoBindOption {
+					prunedOptions = append(prunedOptions, option)
+				}
+			}
+			spec.Mounts[i].Options = prunedOptions
+		}
+	}
+}
+
+func dedupeStringSlice(slice []string) []string {
+	done := make([]string, 0, len(slice))
+	m := make(map[string]struct{})
+	for _, s := range slice {
+		if _, present := m[s]; !present {
+			m[s] = struct{}{}
+			done = append(done, s)
+		}
+	}
+	return done
+}