Added HasAll utility method for string set.

Added HasAll method which detects if one set contains all
of the memebers of another set.

A.HasAll(B) returns true if A is a superset of B.

pkg/util/set.go

@@ -50,6 +50,16 @@ func (s StringSet) Has(item string) bool {
 	return contained
 }
 
+// HasAll returns true iff all items are contained in the set.
+func (s1 StringSet) HasAll(s2 StringSet) bool {
+	for item, _ := range s2 {
+		if !s1.Has(item) {
+			return false
+		}
+	}
+	return true
+}
+
 // List returns the contents as a sorted string slice.
 func (s StringSet) List() []string {
 	res := make([]string, 0, len(s))