Fix hosts.toml template for containerd

The issue is that playbook that configures containerd
defines buildset registry namespace w/o skip_verify
parameter which leads to the error in the template.

This change add additional check whether skip_verify
parameter is defined or not.

Change-Id: I7b6f19d4fe881e33fef2370bac887e9cd66c7b35

tools/gate/playbooks/files/hosts.toml

@@ -7,6 +7,6 @@ capabilities = ["pull", "resolve", "push"]
 {% if item.ca is defined %}
 ca = "{{ item.ca }}"
 {% endif %}
-{% if item.skip_verify %}
+{% if item.skip_verify is defined and item.skip_verify %}
 skip_verify = true
 {% endif %}