avocado.plugins.tap: Fix the CLI import

The plugin base import location changed to `avocado.core`.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

avocado/plugins/tap.py

@@ -18,7 +18,7 @@ TAP output module.
 import logging
 
 from ..core.result import register_test_result_class, TestResult
-from .base import CLI
+from avocado.core.plugin_interfaces import CLI
 
 
 class TAPResult(TestResult):