add policy open_usage

This policy will be used for certificate with various keyUsage
parameters. Etcd for example.

Change-Id: I2a6387f8b7ee58fb6f256881e3e09142f13119a9

salt/files/_pki.conf

@@ -36,6 +36,8 @@ x509_signing_policies:
     {%- elif signing_policy.type == 'v3_edge_ca' %}
     - basicConstraints: "CA:TRUE,pathlen:0"
     - keyUsage: "critical cRLSign,keyCertSign"
+    {%- elif signing_policy.type == 'v3_edge_cert_open' %}
+    - basicConstraints: "CA:FALSE"
     {%- endif %}
     - subjectKeyIdentifier: hash
     - authorityKeyIdentifier: keyid,issuer:always