Move ldap test server to its own package

backend/model_test.go

ldaptest/ldap_server.go

ldaptest/unboundid-ldap-server/bin/unboundid-ldap-server

ldaptest/unboundid-ldap-server/bin/unboundid-ldap-server.bat

ldaptest/unboundid-ldap-server/lib/commons-cli-1.3.1.jar

ldaptest/unboundid-ldap-server/lib/commons-io-2.4.jar

ldaptest/unboundid-ldap-server/lib/commons-logging-1.2.jar

ldaptest/unboundid-ldap-server/lib/ldaptive-1.1.0.jar

ldaptest/unboundid-ldap-server/lib/ldaptive-beans-1.1.0.jar

...st/unboundid-ldap-server/lib/ldaptive-unboundid-1.1.0.jar

ldaptest/unboundid-ldap-server/lib/log4j-api-2.3.jar

ldaptest/unboundid-ldap-server/lib/log4j-core-2.3.jar

ldaptest/unboundid-ldap-server/lib/log4j-jcl-2.3.jar

ldaptest/unboundid-ldap-server/lib/log4j-slf4j-impl-2.3.jar

ldaptest/unboundid-ldap-server/lib/slf4j-api-1.7.12.jar

...t/unboundid-ldap-server/lib/spring-core-4.2.1.RELEASE.jar

ldaptest/unboundid-ldap-server/lib/unboundid-ldap-server.jar

...est/unboundid-ldap-server/lib/unboundid-ldapsdk-3.1.1.jar