boot-initrd from maas images do not have bcache modules

I tried to do the following, and saw failure to install.

$ NAME=maas-1-10; NODE=node-06e710b4-6bcd-11e5-86f5-000e1e989680
$ maas smoser node set-storage-layout $NODE storage_layout=bcache
$ maas smoser nodes acquire name=$NAME
$ maas smoser node start $NODE hwe_kernel=hwe-v

The failure looks lilke this: http://paste.ubuntu.com/13103489/

specifically, you see the hwe-v kernel booted and then:
....
The operation has completed successfully.
Warning: The resulting partition is not properly aligned for best performance.
The operation has completed successfully.
modprobe: FATAL: Module bcache not found.
An error occured handling 'bcache32': ProcessExecutionError - Unexpected error while running command.
Command: ['modprobe', 'bcache']
Exit code: 1
Reason: -
Stdout: ''
Stderr: ''
Unexpected error while running command.
Command: ['modprobe', 'bcache']
Exit code: 1
Reason: -
Stdout: ''
Stderr: ''