[memcached] add funcs to return quoted serverList and update test helpers

[stuggi]

For tls, in #192 changed the server lists to contain the svc fqdn, but missed to update the test helpers.

[abays]

/lgtm

[openshift-ci]

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[softwarefactory-project-zuul]

Build failed (check pipeline). Post recheck (without leading slash)
to rerun all jobs. Make sure the failure cause has been resolved before
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https://review.rdoproject.org/zuul/buildset/60a22c88fb604607823fed44c04f7cbe

✔️ openstack-k8s-operators-content-provider SUCCESS in 1h 29m 32s
✔️ podified-multinode-edpm-deployment-crc SUCCESS in 1h 06m 57s
❌ cifmw-crc-podified-edpm-baremetal RETRY_LIMIT in 4s

[abays]

recheck