tests: Limit use of SPICE TLS

tests: Limit use of SPICE TLS

Follow the example of other similar settings and only enable it
for the few test cases that are actually about the specific
functionality, disabling it immediately afterwards.

A few test cases that were completely unrelated to SPICE TLS no
longer see the effects of having the feature enabled.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>