Panic when deleting collection and kubectl delete hangs

[timterle]

Describe the bug
When deleting a collection the command hangs and solr operator log shows a panic.

To Reproduce
kubectl delete -f solrcollection.yaml

The log says

2020-03-25T17:05:28.980Z	DPANIC	controller	odd number of arguments passed as key-value pairs for logging	{"ignored key": "collection"}
github.com/go-logr/zapr.handleFields
	/go/pkg/mod/github.com/go-logr/zapr@v0.1.0/zapr.go:106
github.com/go-logr/zapr.(*zapLogger).Error
	/go/pkg/mod/github.com/go-logr/zapr@v0.1.0/zapr.go:129
github.com/bloomberg/solr-operator/controllers/util.DeleteCollection
	/workspace/controllers/util/collection_util.go:106
github.com/bloomberg/solr-operator/controllers.(*SolrCollectionReconciler).Reconcile
	/workspace/controllers/solrcollection_controller.go:99
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).reconcileHandler