Tango::Util: add more calls to release GIL

Yury Matveevrequested to merge
add-util-calls-to-release-gil into develop

Related to #627

I added the following calls to release GIL:

Tango::Util::unregister_server
Tango::Util::get_dserver_device
Tango::Util::server_cleanup
Tango::Util::trigger_cmd_polling
Tango::Util::trigger_attr_polling
Tango::Util::connect_db
Tango::Util::reset_filedatabase
Tango::Util::get_device_list_by_class
Tango::Util::get_device_by_name
Tango::Util::get_device_list

This solves block in #627 (comment 2089503324)

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