add timeout parameter to wait-for-it script; refs DE-347

this parameter is added for easier testing of postgres spin up
timeouts.

flag=none

test plan:
* wait-for-it still behaves as expected and defaults to 60 seconds.

Change-Id: Iec8c704f68bf36941ffea043ed5c942b3e70d758
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/251499
Reviewed-by: Andrea Cirulli <andrea.cirulli@instructure.com>
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
QA-Review: Kyle Rosenbaum <krosenbaum@instructure.com>
Product-Review: Kyle Rosenbaum <krosenbaum@instructure.com>

docker-compose/postgres/wait-for-it

@@ -3,10 +3,13 @@
 set -x
 
 ip_address=$(hostname -i)
-echo Attempting connection to postgres...
-for _ in {1..60}; do
+timeout=${1:-60}
+
+echo Attempting connection to Postgres for $timeout seconds...
+for _ in $(seq 1 $timeout); do
   gosu postgres pg_isready --host="$ip_address" && echo "Postgres connected!" && exit
   sleep 1
 done
-echo Postgres is still down after 60 seconds.
+
+echo Postgres is still down after $timeout seconds.
 exit 1