Upgrade CAPG to version v0.3.1 with Cluster API v1alpha4 support

[eak13]

Problem description
In an effort to keep Airship current with the latest updates of its supporting components, upgrade the CAPG (Cluster-API for GCP provider) to v0.3.1 with Cluster API v1alpha4 support. The current GCP Provider is v0.3.0.

CAPG github repo can be found here: https://github.com/kubernetes-sigs/cluster-api-provider-gcp

Proposed change

• Upgrade CAPG version to v0.3.1 with Cluster API v1alpha4 support
• Validate CAPG still functional as the the infra provider for GCP & resolve any breaking changes

[ratnopam]

I can take this one.

[ratnopam]

Please assign size L. Thanks.