data/aws/vpc/master-elb: Bump load-balancer timeouts to 20m

Up from their default 10 minutes, using the knob that dates back to
the original network load balancer support [1].  This should help us
avoid the [2]:

  Error: timeout while waiting for state to become 'active' (last state: 'provisioning', timeout: 10m0s)

that cropped up again this week.  20m matches the timeout we set for
routes and security groups in 246f4a1 (data/aws: 20-minute create
timeouts for routes and security groups, 2019-04-26, openshift#1682).
Sometimes even 20m will not be enough [3], but should make us a bit
more resilient anyway.

[1]: hashicorp/terraform-provider-aws@1af53b1#diff-f4b0dbdc7e3eede6ba70cd286c834f37R92
[2]: https://bugzilla.redhat.com/show_bug.cgi?id=1717604
[3]: https://bugzilla.redhat.com/show_bug.cgi?id=1717604#c15

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

@@ -13,6 +13,10 @@ resource "aws_lb" "api_internal" {
     var.tags,
   )
 
+  timeouts {
+    create = "20m"
+  }
+
   depends_on = [aws_internet_gateway.igw]
 }
 
@@ -31,6 +35,10 @@ resource "aws_lb" "api_external" {
     var.tags,
   )
 
+  timeouts {
+    create = "20m"
+  }
+
   depends_on = [aws_internet_gateway.igw]
 }