aaa: Convert list of ldap server names to URIs

Convert list of ldap server names contained in ConfigValue.LdapServers
to list of URIs stored in extension config under key "config.LdapServers"
during kerberosldap extension startup.

Topic: AAA
Change-Id: Ic436192e0072af09c4be1cfaa78c9e5bb66743ad
Bug-Url: https://bugzilla.redhat.com/1111071
Signed-off-by: Martin Perina <mperina@redhat.com>