ldap: ws cleanups, test load ldapjs in register,

only register hook if ldapjs loads
ldap: support per-domain LDAP params
ldap: make sure domain exists before using it
move host_list functions into host_list_base

* updated rcpt_to.in_host_list and rcpt_to.ldap accordingly
* added tests for base + 2 plugins
Merge pull request #721 from msimerson/rcpt.ldap

LDAP: ws cleanups, test load ldapjs in register,