Do not sent fault domain if failure domain is set as empty

[shyamradhakrishnan]

What this PR does / why we need it:
Do not sent fault domain if failure domain is set as empty. OCI Compute will select the right fault domain based on various factors.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #351

[shyamradhakrishnan]

e2e

[SynchronizedAfterSuite]
/home/ubuntu/go/src/github.com/oracle/cluster-api-provider-oci/test/e2e/e2e_suite_test.go:261

  Timeline >>
  STEP: Tearing down the management cluster @ 03/01/24 06:38:11.415
  << Timeline
------------------------------

Ran 7 of 28 Specs in 3188.165 seconds
SUCCESS! -- 7 Passed | 0 Failed | 0 Pending | 21 Skipped

[shyamradhakrishnan]

unit test

$ make test
GOBIN=/home/ubuntu/go/src/github.com/oracle/cluster-api-provider-oci/hack/tools/bin ./scripts/go_install.sh sigs.k8s.io/controller-runtime/tools/setup-envtest setup-envtest v0.0.0-20230131074648-f5014c077fc3
^[[Okube-builder assets: /home/ubuntu/.local/share/kubebuilder-envtest/k8s/1.24.2-linux-amd64
KUBEBUILDER_ASSETS="/home/ubuntu/.local/share/kubebuilder-envtest/k8s/1.24.2-linux-amd64" go test -coverprofile=coverage.out ./...
^[[I^[[O^[?   	github.com/oracle/cluster-api-provider-oci	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/config	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/metrics	[no test files]
^[[O^[[I^[[Ook  	github.com/oracle/cluster-api-provider-oci/api/v1beta1	62.317s	coverage: 23.7% of statements
ok  	github.com/oracle/cluster-api-provider-oci/api/v1beta2	0.043s	coverage: 15.6% of statements
ok  	github.com/oracle/cluster-api-provider-oci/cloud/ociutil	0.020s	coverage: 19.6% of statements
?   	github.com/oracle/cluster-api-provider-oci/cloud/scope/mocks	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/base	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/base/mock_base	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/compute	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/compute/mock_compute	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/computemanagement	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/computemanagement/mock_computemanagement	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/containerengine	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/containerengine/mock_containerengine	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/identity	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/identity/mock_identity	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/loadbalancer	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/loadbalancer/mock_lb	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/networkloadbalancer	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/networkloadbalancer/mock_nlb	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/vcn	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/cloud/services/vcn/mock_vcn	[no test files]
^[[I^[[O?   	github.com/oracle/cluster-api-provider-oci/feature	[no test files]
?   	github.com/oracle/cluster-api-provider-oci/version	[no test files]
^[[I^[[O^[[I^[[Ook  	github.com/oracle/cluster-api-provider-oci/cloud/scope	231.416s	coverage: 75.1% of statements
ok  	github.com/oracle/cluster-api-provider-oci/cloud/util	0.278s	coverage: 61.1% of statements
ok  	github.com/oracle/cluster-api-provider-oci/controllers	26.860s	coverage: 58.7% of statements
ok  	github.com/oracle/cluster-api-provider-oci/exp/api/v1beta1	15.907s	coverage: 15.3% of statements
ok  	github.com/oracle/cluster-api-provider-oci/exp/api/v1beta2	0.018s	coverage: 4.8% of statements
ok  	github.com/oracle/cluster-api-provider-oci/exp/controllers	0.386s	coverage: 56.3% of statements
go tool cover -func=coverage.out -o coverage.txt
go tool cover -html=coverage.out -o coverage.html