gitignore: add test/etcd-client

This directory belongs to the EE repository.

Also, delete test/enterprise-tap because we don't have any TAP tests in
the EE repository.

Follow-up commit d8faca69 ("lua: implement stubs for etcd client").

NO_DOC=gitignore
NO_TEST=gitignore
NO_CHANGELOG=gitignore

.gitignore

@@ -95,8 +95,8 @@ src/module.h
 tarantool-*.tar.gz
 perf/*.perftest
 test/enterprise-luatest
-test/enterprise-tap
 test/enterprise-unit
+test/etcd-client
 test/lib/
 test/unit/*.test
 test/unit/fiob