data/aws/vpc/master-elb: Set thresholds back to two

These were changes from two to three in 16dfbb3 (data/aws: use nlbs
instead of elbs, 2019-11-01, openshift#594):

  $ git show 16dfbb3 | grep _threshold | sort | uniq
  -    healthy_threshold   = 2
  -  #   healthy_threshold   = 2
  +    healthy_threshold   = 3
  -    unhealthy_threshold = 2
  -  #   unhealthy_threshold = 2
  +    unhealthy_threshold = 3

Alex doesn't remember intentionally making that change, and the lower
thresholds will hopefully help mitigate some issues with continued
connection attempts to API servers which are in the process of
shutting down.

data/data/aws/vpc/master-elb.tf

@@ -41,8 +41,8 @@ resource "aws_lb_target_group" "api_internal" {
   ), var.tags)}"
 
   health_check {
-    healthy_threshold   = 3
-    unhealthy_threshold = 3
+    healthy_threshold   = 2
+    unhealthy_threshold = 2
     interval            = 10
     port                = 6443
     protocol            = "HTTPS"
@@ -63,8 +63,8 @@ resource "aws_lb_target_group" "api_external" {
   ), var.tags)}"
 
   health_check {
-    healthy_threshold   = 3
-    unhealthy_threshold = 3
+    healthy_threshold   = 2
+    unhealthy_threshold = 2
     interval            = 10
     port                = 6443
     protocol            = "HTTPS"
@@ -85,8 +85,8 @@ resource "aws_lb_target_group" "services" {
   ), var.tags)}"
 
   health_check {
-    healthy_threshold   = 3
-    unhealthy_threshold = 3
+    healthy_threshold   = 2
+    unhealthy_threshold = 2
     interval            = 10
     port                = 22623
     protocol            = "HTTPS"