tests: Keep ZEO test database on /tmp/

We already keep FileStorage test database on /tmp/ and NEO itself (via
neo.tests.functional.NEOCluster) also keeps test data on tmpfs. However
test database for ZEO was created in current directory and was wearing
out SSD unnecessarily.

FIXME zeo_forker currently does not provide API to keep all server files
in particular place. This way server conf and log are still emitted in
current directory, but at least we move data.fs away. Since conf and log
are uniquely named, e.g. server-<ΧΧΧ>.conf and tmpYYY.log, and it was
only that Data.fs was named non-uniquely, by moving Data.fs into unique
per-server place, this also helps with-ZEO tests to execute correctly in
parallel with `tox -p`.

lib/testing.py

 # Wendelin. Testing utilities
-# Copyright (C) 2014-2015  Nexedi SA and Contributors.
+# Copyright (C) 2014-2019  Nexedi SA and Contributors.
 #                          Kirill Smelkov <kirr@nexedi.com>
 #
 # This program is free software: you can Use, Study, Modify and Redistribute
@@ -259,9 +259,11 @@ class TestDB_ZEO(TestDB_Base):
 
 
     def setup(self):
+        self.tmpd = mkdtemp('', 'testdb_zeo.')
+
         port  = self.zeo_forker.get_port()
         zconf = self.zeo_forker.ZEOConfig(('', port))
-        _ = self.zeo_forker.start_zeo_server(zeo_conf=zconf, port=port)
+        _ = self.zeo_forker.start_zeo_server(path='%s/1.fs' % self.tmpd, zeo_conf=zconf, port=port)
         if self.z5:
             self.addr, self.stop = _
         else:
@@ -274,6 +276,8 @@ class TestDB_ZEO(TestDB_Base):
             self.zeo_forker.shutdown_zeo_server(self.adminaddr)
             os.waitpid(self.pid, 0)
 
+        rmtree(self.tmpd)
+
     def getZODBStorage(self):
         from ZEO.ClientStorage import ClientStorage
         return ClientStorage(self.addr)