Katib DB readinessProbe should specify user explicitly

[vpavlin]

/kind bug

What steps did you take and what happened:

Deploy Katib using kfctl on OpenShift 4.x

OpenShift runs containers as non-root users by default for security reasons. If that happens the readinessProbe in Katib DB deployment will fail because the command will pick up the container user instead of root

mysql -D ${MYSQL_DATABASE} -p${MYSQL_ROOT_PASSWORD} -e 'SELECT 1'

It would be ideal to add -u root explicitly

This issue has already been reported here: #361

What did you expect to happen:

readinessProbe should succeed even if the db is not running as root

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

Environment:

OpenShift 4.x