Fix tests on memcached_current_connections
Fix tests on memcached_current_connections

Depending on the version of memcached that is used for testing, the
value of memcached_current_connections varies. This change only checks
that memcached_current_connections metric is returned by the exporter
but it doesn't assert its value.

Signed-off-by: Simon Pasquier <38e2d22e48be18381a59028f88390cad04670376@redhat.com>

prometheus/memcached_exporter