make SetExpire public, so that expiry date can be computed (#723)
make SetExpire public, so that expiry date can be computed (#723)


GoogleCloudPlatform/compute-image-tools,zmarano/compute-image-tools,GoogleCloudPlatform/compute-image-import,adjackura/compute-image-tools,GoogleCloudPlatform/compute-image-tools,adjackura/compute-image-tools,adjackura/compute-image-tools,GoogleCloudPlatform/compute-daisy,GoogleCloudPlatform/compute-image-tools,GoogleCloudPlatform/compute-daisy,GoogleCloudPlatform/compute-image-import,zmarano/compute-image-tools,GoogleCloudPlatform/compute-image-import,zmarano/compute-image-tools