Fix out-of-date test expectations

What does this MR do?

It fixes a couple of integration test expectations I noticed were failing when running make test.

Why was this MR needed?

Code has been changed without adapting the test expectation strings, and since these tests are skipped in CI, we didn't notice it.

$ exit 1
Running after_script
Uploading artifacts for failed job
ERROR: Job failed: Process exited with status 1
--- FAIL: TestVirtualBoxBuildFail (29.09s)
    virtualbox_test.go:117: 
                Error Trace:    virtualbox_test.go:117
                Error:          "Process exited with status 1" does not contain "Process exited with: 1"
                Test:           TestVirtualBoxBuildFail
Running with gitlab-runner development version (HEAD)
Preparing the "virtualbox" executor

ERROR: Job failed (system failure): missing SSH config
--- FAIL: TestVirtualBoxMissingSSHCredentials (9.04s)
    virtualbox_test.go:162: 
                Error Trace:    virtualbox_test.go:162
                Error:          "missing SSH config" does not contain "Missing SSH config"
                Test:           TestVirtualBoxMissingSSHCredentials

Also a few assert.IsType calls have their arguments reversed:

   --- FAIL: TestRunTestsWithFeatureFlag/testKubernetesMissingTag_FF_USE_LEGACY_KUBERNETES_EXECUTION_STRATEGY_false (9.19s)
        kubernetes_test.go:659: 
                Error Trace:    kubernetes_test.go:659
                                                        kubernetes_test.go:77
                Error:          Object expected to be of type *fmt.wrapError, but was *common.BuildError
                Test:           TestRunTestsWithFeatureFlag/testKubernetesMissingTag_FF_USE_LEGACY_KUBERNETES_EXECUTION_STRATEGY_false

Are there points in the code the reviewer needs to double check?

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Added tests for this feature/bug
• In case of conflicts with master - branch was rebased

What are the relevant issue numbers?

#1829