use a variable for the branch to use for the AMI script repo
diff --git a/build-aws-amis.yaml b/build-aws-amis.yaml
index 7f1c005..1b977a8 100644
--- a/build-aws-amis.yaml
+++ b/build-aws-amis.yaml
@@ -33,6 +33,10 @@
         name: BUILD_CUSTOM_AMI
         default: false
         description: Build Custom AMI
+    - string:
+        name: AMI_REPO_BRANCH
+        default: master
+        description: Branch to use when cloning git.trustedfirmware.org/ci/aws-amis.git
     builders:
         - shell: |
             #!/bin/bash
@@ -48,7 +52,7 @@
             [ -z "${AMI}" ] && echo "Build Nothing.." && exit
 
             [ -d "aws-amis" ] && rm -rf aws-amis
-            git clone https://git.trustedfirmware.org/ci/aws-amis.git -b openci-migration
+            git clone https://git.trustedfirmware.org/ci/aws-amis.git -b $AMI_REPO_BRANCH
             cd aws-amis
 
             for os in ${AMI}