e2e: add weighted random configuration selector (#6869)

When revwing #6807 I assumed that `probSetChoice` worked this way. 

I think that the coverage of various configuration options should
generally track what we expect the actual useage to be to focus the
most test coverage on the configurations that are the most prevelent.

test/e2e/generator/generate.go

@@ -26,7 +26,13 @@ var (
 	}
 
 	// The following specify randomly chosen values for testnet nodes.
-	nodeDatabases        = uniformChoice{"goleveldb", "cleveldb", "rocksdb", "boltdb", "badgerdb"}
+	nodeDatabases = weightedChoice{
+		"goleveldb": 35,
+		"badgerdb":  35,
+		"boltdb":    15,
+		"rocksdb":   10,
+		"cleveldb":  5,
+	}
 	nodeABCIProtocols    = uniformChoice{"unix", "tcp", "builtin", "grpc"}
 	nodePrivvalProtocols = uniformChoice{"file", "unix", "tcp", "grpc"}
 	// FIXME: v2 disabled due to flake
@@ -270,7 +276,7 @@ func generateNode(
 	node := e2e.ManifestNode{
 		Mode:             string(mode),
 		StartAt:          startAt,
-		Database:         nodeDatabases.Choose(r).(string),
+		Database:         nodeDatabases.Choose(r),
 		ABCIProtocol:     nodeABCIProtocols.Choose(r).(string),
 		PrivvalProtocol:  nodePrivvalProtocols.Choose(r).(string),
 		BlockSync:        nodeBlockSyncs.Choose(r).(string),
@@ -321,7 +327,7 @@ func generateLightNode(r *rand.Rand, startAt int64, providers []string) *e2e.Man
 	return &e2e.ManifestNode{
 		Mode:            string(e2e.ModeLight),
 		StartAt:         startAt,
-		Database:        nodeDatabases.Choose(r).(string),
+		Database:        nodeDatabases.Choose(r),
 		ABCIProtocol:    "builtin",
 		PersistInterval: ptrUint64(0),
 		PersistentPeers: providers,

test/e2e/generator/random.go

@@ -3,6 +3,8 @@ package main
 import (
 	"math/rand"
 	"sort"
+
+	"github.com/mroth/weightedrand"
 )
 
 // combinations takes input in the form of a map of item lists, and returns a
@@ -83,3 +85,19 @@ func (usc uniformSetChoice) Choose(r *rand.Rand) []string {
 	}
 	return choices
 }
+
+type weightedChoice map[string]uint
+
+func (wc weightedChoice) Choose(r *rand.Rand) string {
+	choices := make([]weightedrand.Choice, 0, len(wc))
+	for k, v := range wc {
+		choices = append(choices, weightedrand.NewChoice(k, v))
+	}
+
+	chooser, err := weightedrand.NewChooser(choices...)
+	if err != nil {
+		panic(err)
+	}
+
+	return chooser.PickSource(r).(string)
+}