K8SPSMDB-1296: improve readiness probe

[pooknull]

https://perconadev.atlassian.net/browse/K8SPSMDB-1296

CHANGE DESCRIPTION

Problem:
Short explanation of the problem.

Cause:
Short explanation of the root cause of the issue if applicable.

Solution:
Short explanation of the solution we are providing with this PR.

CHECKLIST

Jira

• Is the Jira ticket created and referenced properly?
• Does the Jira ticket have the proper statuses for documentation (Needs Doc) and QA (Needs QA)?
• Does the Jira ticket link to the proper milestone (Fix Version field)?

Tests

• Is an E2E test/test case added for the new feature/change?
• Are unit tests added where appropriate?
• Are OpenShift compare files changed for E2E tests (compare/*-oc.yml)?

Config/Logging/Testability

• Are all needed new/changed options added to default YAML files?
• Are all needed new/changed options added to the Helm Chart?
• Did we add proper logging messages for operator actions?
• Did we ensure compatibility with the previous version or cluster upgrade process?
• Does the change support oldest and newest supported MongoDB version?
• Does the change support oldest and newest supported Kubernetes version?

[JNKPercona]

Test name	Status
arbiter	failure
balancer	passed
cross-site-sharded	passed
custom-replset-name	passed
custom-tls	failure
custom-users-roles	passed
custom-users-roles-sharded	failure
data-at-rest-encryption	failure
data-sharded	failure
demand-backup	failure
demand-backup-eks-credentials-irsa	passed
demand-backup-fs	failure
demand-backup-incremental	failure
demand-backup-incremental-sharded	failure
demand-backup-physical	failure
demand-backup-physical-sharded	failure
demand-backup-sharded	failure
expose-sharded	failure
finalizer	passed
ignore-labels-annotations	passed
init-deploy	failure
ldap	passed
ldap-tls	passed
limits	failure
liveness	passed
mongod-major-upgrade	passed
mongod-major-upgrade-sharded	failure
monitoring-2-0	failure
multi-cluster-service	passed
multi-storage	passed
non-voting	failure
one-pod	failure
operator-self-healing-chaos	passed
pitr	failure
pitr-physical	failure
pitr-sharded	failure
pitr-physical-backup-source	failure
preinit-updates	passed
pvc-resize	failure
recover-no-primary	passed
replset-overrides	passed
rs-shard-migration	failure
scaling	passed
scheduled-backup	failure
security-context	failure
self-healing-chaos	failure
service-per-pod	failure
serviceless-external-nodes	failure
smart-update	failure
split-horizon	passed
stable-resource-version	failure
storage	failure
tls-issue-cert-manager	failure
upgrade	failure
upgrade-consistency	failure
upgrade-consistency-sharded-tls	passed
upgrade-sharded	passed
users	passed
version-service	failure
We run 59 out of 59

commit: d6e9d6b
image: perconalab/percona-server-mongodb-operator:PR-1917-d6e9d6b1