Add possible to pkg sandbox to be usable in docker tests

[denis-tingaikin]

Description

Currently many and many cmd-apps doing the same setup for registry memory or for emulating manager in each test that making reading and supporting tests difficult.

Examples:

1. https://github.com/networkservicemesh/cmd-nsmgr/blob/master/test/client_endpoint_test.go#L64-L192
2. https://github.com/networkservicemesh/cmd-nse-icmp-responder/blob/master/suite_setup_test.go#L103-L152
3. https://github.com/networkservicemesh/cmd-forwarder-vpp/blob/master/internal/tests/suite_setup_test.go#L121-L191

Solution

1. Add possible to sandbox pass additional dial options to use transport creds with spire cert.
2. Use sandbox around the testing application.

[denis-tingaikin]

@edwarnicke Is this make sense?

[Bolodya1997]

Blocked by #870.