The multiarch validator should not warning when only linux.amd64 platform is found

[camilamacedo86]

Example:

$ operator-sdk bundle validate ./testdata/go/v3/memcached-operator/bundle/ --select-optional name=multiarch 
WARN[0017] Warning: Value memcached-operator.v0.0.1: unable to inspect the image (quay.io/example/memcached-operator:v0.0.1) : docker pull quay.io/example/memcached-operator:v0.0.1 failed with error: (exit status 1) Error response from daemon: unauthorized: access to the requested resource is not authorized 
WARN[0017] Warning: Value memcached-operator.v0.0.1: unable to inspect the image (gcr.io/kubebuilder/kube-rbac-proxy:v0.12.0) : docker manifest inspect gcr.io/kubebuilder/kube-rbac-proxy:v0.12.0 failed with error: (exit status 1) Get "https://gcr.io/v2/kubebuilder/kube-rbac-proxy/manifests/v0.12.0": unauthorized: You don't have the needed permissions to perform this operation, and you may have invalid credentials. To authenticate your request, follow the steps in: https://cloud.google.com/container-registry/docs/advanced-authentication 
WARN[0017] Warning: Value memcached-operator.v0.0.1: check if the CSV is missing the label (operatorframework.io/arch.<value>) for the Arch(s): ["amd64"]. Be aware that your Operator manager image ["quay.io/example/memcached-operator:v0.0.1"] provides this support. Thus, it is very likely that you want to provide it and if you support more than amd64 architectures, you MUST,use the required labels for all which are supported.Otherwise, your solution cannot be listed on the cluster for these architectures 
WARN[0017] Warning: Value memcached-operator.v0.0.1: check if the CSV is missing the label (operatorframework.io/os.<value>) for the SO(s): ["linux"]. Be aware that your Operator manager image ["quay.io/example/memcached-operator:v0.0.1"] provides this support. Thus, it is very likely that you want to provide it and if you support more than linux SO you MUST,use the required labels for all which are supported.Otherwise, your solution cannot be listed on the cluster for these architectures 
INFO[0017] All validation tests have completed successfully 

PS.: It probably only occurs when we also are unable to inspect some image and we face errors

[camilamacedo86]

/assign @camilamacedo86