toolbox: bump test VM memory for current CoreOS release
toolbox: bump test VM memory for current CoreOS release

The current releases fail to boot with 1G memory, bump to 2G.

Switch to stable coreos release.

vmware/govmomi,vmware/govmomi,bruceadowns/govmomi,bruceadowns/govmomi,vmware/govmomi,bruceadowns/govmomi