Comment 8 for bug 1514094

Taking over from Scott/Ryan as we are less "thankfully giving" these days in
Europe.

Looking at the testcase we had for bcache, the description blake_r was giving
us and some "mean tester thinking" I ended up adding:
- non ordered ids 1, 0 (base on blake_r)
- caching with a partition-less device (base on blake_r)
- backing a partition-less device
- use all different cache modes
I also thought on stacking, but they are discouraged reading upstream, so I
skipped those for now.
- backing with a bcache device (stacking)
- caching with a bcache device (stacking)

We might also add this further on:
- putting / on bcached device (base on blake_r)

Recreation of the issue worked - commented serial of install log:
http://paste.ubuntu.com/13495607/
(look for CE: for my comments)

With the debugging commented in the log the fix looked rather simple
(as always when you know whats going on)
- '/sys/block/{}/bcache/cache_mode'.format(info.get('id'))
+ '/sys/block/{}/bcache/cache_mode'.format(bcache_dev)

The enhanced test I defined fully ran through installation with this fix.
I was also able to adapt all the assertions of the test to cover the new
definitions properly - and they work even in this more complex setup.

Later I also added the "/ on bcache" to further enhance the testcase, but
this is failing on grub install now.
That means this is not final yet, but at some point I have to sleep :-)

MAAS Team, if you can feel free to help me testing using this branch
=> lp:~paelzer/curtin/fix-1514094-v1
If you stop at:
"Command: ['install-grub', '/tmp/tmp8mjp2u0k/target', '/dev/bcache2']"
this is what I'm debugging atm anyway - anything else please let me know.

If I hear nothing I'll let you all know once I'm happy with the extended
testing.