gerrit secure.config.erb - variable access

from puppet compiler warnings on ytterbium:

Variable access via 'ldap_proxyagent_pass' is deprecated. Use '@ldap_proxyagent_pass' instead.
Variable access via 'ldap_proxyagent' is deprecated. Use '@ldap_proxyagent' instead.

Change-Id: Ic4eb2051b28c39ec7ffaef718e0c256386f963bf
Merge "gerrit secure.config.erb - variable access" into production