[V124-specific] semi random asgard vault selection based on tx inhash and block height

closes:#1718 (closed)
hashes tx inhash and block height to generate a semi-random number to be used for Asgard vault selection

common/random_string.go

@@ -2,7 +2,7 @@ package common
 
 import "math/rand"
 
-const letterBytes = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+const letterBytes = "abcdefABCDEF0123456789"
 const (
 	letterIdxBits = 6                    // 6 bits to represent a letter index
 	letterIdxMask = 1<<letterIdxBits - 1 // All 1-bits, as many as letterIdxBits