expect! in status() methods will probably lead to embarassment eventually

[mulkieran]

The argument for the expects is that devicemapper should be notified well ahead of time of any change to the format of the output. But, given that the docs in the kernel right now don't correctly or fully describe the current format, what we're really doing is iteratively discovering the format, and we should expect that process to be indefinite.

stratisd shouldn't crash because of unexpected values in status output, and it has already. Let's be more realistic and make status() methods return a Result type.

[mulkieran]

Well, status() methods already return a Result because getting dm status might fail. Let's also have them return an Err on parse failure.

[mulkieran]

Probably best to leave this until error-handling is completed sensibly.