[google][compute] Update to API v1

Simplify attachment of boot disk, get_as_boot_disk no longer needed
Add missing Disk.get_object method
Allow setting deviceName when attaching a disk
Add disks mocks
[google] Handle 500 errors from GCE
[google][compute] Add support for blank disks (i.e. remove code that required only image or snapshot based disks to be created)
Merge branch 'gce-v1' into maestrodev

Conflicts:
	lib/fog/google/models/compute/disk.rb
	lib/fog/google/requests/compute/insert_disk.rb
	tests/google/models/compute/servers_tests.rb