util: Add errwrap package

Simplify working with errors across our code base. Instead of constantly
importing the necessary error helpers, assemble them all into one
package and import and use that as needed.

test/test-govet.sh

@@ -50,6 +50,10 @@ function naked-error() {
 }
 
 function consistent-imports() {
+	if [ "$1" = './util/errwrap/errwrap.go' ]; then
+		return 0
+	fi
+
 	if grep $'\t"github.com/pkg/errors"' "$1"; then	# import as errwrap
 		return 1
 	fi