e2e: add prerelease builds to Consul/Vault compatibility tests (#23287)

Update the Consul/Vault build downloader functions so that we include the
current prerelease build (if any) in our E2E compatibility testing we do on each
PR. This will automatically cycle out when the GA build is released, because
that build is "higher" in the sorted set.

e2e/consulcompat/run_ce_test.go

@@ -16,12 +16,10 @@ import (
 // versions of Consul CE
 func usable(v, minimum *version.Version) bool {
 	switch {
-	case v.Prerelease() != "":
+	case v.LessThan(minimum):
 		return false
 	case v.Metadata() != "":
 		return false
-	case v.LessThan(minimum):
-		return false
 	default:
 		return true
 	}

e2e/consulcompat/shared_download_test.go

@@ -19,9 +19,6 @@ import (
 	"github.com/shoenig/test/must"
 )
 
-// TODO: it would be good if we can add the latest non-GA'd beta/release
-// candidate version as well; that'll give us some lead time on any breaking
-// changes
 const (
 	binDir           = "consul-bins"
 	minConsulVersion = "1.16.0"

e2e/vaultcompat/run_ce_test.go

@@ -17,8 +17,6 @@ import (
 // versions of Vault CE
 func usable(v, minimum *version.Version) bool {
 	switch {
-	case v.Prerelease() != "":
-		return false
 	case v.Metadata() != "":
 		return false
 	case v.LessThan(minimum):