Skip LDAP tests if LDAP library isn't available

LDAP *is* marked as an optional dependency, so the test suite should
still complete without it.

tests/unittests/general/webfront_test.py

@@ -170,6 +170,9 @@ def test_remote_user_set(self, fake_session):
                 )
 
 
+@pytest.mark.skipif(
+    not nav.web.auth.ldap.available, reason="ldap module is not available"
+)
 class TestLdapUser(object):
     @patch.dict(
         "nav.web.auth.ldap._config._sections",
@@ -269,6 +272,9 @@ def fake_search(base, scope, filtr):
         },
     },
 )
+@pytest.mark.skipif(
+    not nav.web.auth.ldap.available, reason="ldap module is not available"
+)
 class TestLdapEntitlements(object):
     def test_required_entitlement_should_be_verified(self, user_zaphod):
         u = nav.web.auth.ldap.LDAPUser("zaphod", user_zaphod)

tests/unittests/web/ldapauth_test.py

@@ -1,8 +1,16 @@
+import pytest
+
+import nav.web.auth.ldap
 from nav.config import NAVConfigParser
 from nav.web.auth.ldap import LDAPUser, open_ldap
 from mock import Mock, patch
 
 
+pytestmark = pytest.mark.skipif(
+    not nav.web.auth.ldap.available, reason="ldap module is not available"
+)
+
+
 class LdapTestConfig(NAVConfigParser):
     DEFAULT_CONFIG_FILES = []
     DEFAULT_CONFIG = u"""