Remove any existing salt keys on salt-master bootstrap

cfg01-day01 image comes with pre-configured 'ubuntu-1604'
and 'cfg01.deploy-name.local' minion keys which must be deleted.

Change-Id: I144c66084abe735bd533a3b264a1659e00c6c9ce
diff --git a/tcp_tests/templates/shared-salt.yaml b/tcp_tests/templates/shared-salt.yaml
index d7396b5..11c6380 100644
--- a/tcp_tests/templates/shared-salt.yaml
+++ b/tcp_tests/templates/shared-salt.yaml
@@ -77,6 +77,12 @@
   retry: {count: 1, delay: 1}
   skip_fail: false
 
+- description: Remove any existing minion keys
+  cmd:  salt-key -y -D || true
+  node_name: {{ HOSTNAME_CFG01 }}
+  retry: {count: 1, delay: 1}
+  skip_fail: false
+
 - description: Configure salt-master on cfg01
   cmd: |
     cat << 'EOF' > /etc/salt/master.d/master.conf