[CT] In setup-script create /b/ earlier. Might need it for chromium checkout.

Bug: skia:990725
Change-Id: I08b22591334eb978d1aff7f74becf392b3b2b449
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/233717
Reviewed-by: Ravi Mistry <rmistry@google.com>
Commit-Queue: Ravi Mistry <rmistry@google.com>
diff --git a/go/gce/ct/setup-script.sh b/go/gce/ct/setup-script.sh
index 1c40701..b76aa96 100644
--- a/go/gce/ct/setup-script.sh
+++ b/go/gce/ct/setup-script.sh
@@ -39,6 +39,12 @@
 fi
 PATH=$PATH:~/depot_tools
 
+# Create /b if it does not already exist.
+if [[ ! -d /b ]]; then
+  sudo mkdir /b
+  sudo chown chrome-bot:chrome-bot /b
+fi
+
 # If the bot is a builder then checkout Chromium and Skia repositories.
 if [[ $(hostname -s) = ct-*-builder* ]]; then
   echo "Checking out Chromium repository..."
@@ -77,11 +83,7 @@
 # Get access token from metadata.
 TOKEN=`curl "http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/token" -H "Metadata-Flavor: Google" | python -c "import sys, json; print json.load(sys.stdin)['access_token']"`
 # Bootstrap Swarming.
-if [[ ! -d /b ]]; then
-  sudo mkdir /b
-  sudo chown chrome-bot:chrome-bot /b
-  mkdir -p /b/s
-fi
+mkdir -p /b/s
 SWARMING=https://chrome-swarming.appspot.com
 HOSTNAME=`hostname`
 curl ${SWARMING}/bot_code?bot_id=$HOSTNAME -H "Authorization":"Bearer $TOKEN" -o /b/s/swarming_bot.zip