fail gracefully when client-ca file is not set or doesn't exist

[sjenning]

There is not validation enforcing that the --client-ca flag be set. Even if there was, we are currently eating the error on NewCertPoolStore if, for example, the file does not exist. This results in a nil deref farther down the code path.

The PR returns on error so we gracefully handle the situation.

[openshift-ci]

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[openshift-ci]

@sjenning: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Rerun command
ci/prow/verify	5733569	link	/test verify

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[sjenning]

close in favor of operator-framework/operator-lifecycle-manager#2358