Enable construction of TruncIndex from id array.

Fixes #5166

Current graph.restore is essentially O(n^2 log n) due to how
suffixarray creation works.

Rather than create/append/create new this supports creation from a seed
array of ids.

Functional testing shows this eliminates the hang on Creating image
graph reported on list.

Docker-DCO-1.1-Signed-off-by: Paul Nasrat <pnasrat@gmail.com> (github: pnasrat)
Upstream-commit: 4f169c2db512d2ea9ed5729df375896a1ee90347
Component: engine

components/engine/utils/utils_test.go

@@ -138,7 +138,8 @@ func TestRaceWriteBroadcaster(t *testing.T) {
 
 // Test the behavior of TruncIndex, an index for querying IDs from a non-conflicting prefix.
 func TestTruncIndex(t *testing.T) {
-	index := NewTruncIndex()
+	ids := []string{}
+	index := NewTruncIndex(ids)
 	// Get on an empty index
 	if _, err := index.Get("foobar"); err == nil {
 		t.Fatal("Get on an empty index should return an error")