util: Port all code to new errwrap package

This should keep things more uniform.

engine/graph/autogroup/autogroup.go

@@ -22,8 +22,7 @@ import (
 
 	"github.com/purpleidea/mgmt/engine"
 	"github.com/purpleidea/mgmt/pgraph"
-
-	errwrap "github.com/pkg/errors"
+	"github.com/purpleidea/mgmt/util/errwrap"
 )
 
 // AutoGroup is the mechanical auto group "runner" that runs the interface spec.

engine/graph/autogroup/autogroup_test.go

@@ -31,8 +31,7 @@ import (
 	"github.com/purpleidea/mgmt/engine/traits"
 	"github.com/purpleidea/mgmt/pgraph"
 	"github.com/purpleidea/mgmt/util"
-
-	errwrap "github.com/pkg/errors"
+	"github.com/purpleidea/mgmt/util/errwrap"
 )
 
 func init() {

engine/graph/autogroup/nonreachability.go

@@ -19,8 +19,7 @@ package autogroup
 
 import (
 	"github.com/purpleidea/mgmt/pgraph"
-
-	errwrap "github.com/pkg/errors"
+	"github.com/purpleidea/mgmt/util/errwrap"
 )
 
 // NonReachabilityGrouper is the most straight-forward algorithm for grouping.

engine/graph/autogroup/util.go

@@ -19,8 +19,7 @@ package autogroup
 
 import (
 	"github.com/purpleidea/mgmt/pgraph"
-
-	errwrap "github.com/pkg/errors"
+	"github.com/purpleidea/mgmt/util/errwrap"
 )
 
 // VertexMerge merges v2 into v1 by reattaching the edges where appropriate,