Make DmError able to be cloned

[jbaublitz]

Related to straits-storage/stratisd#2664

First, investigate whether this is possible with the error chaining crate. If it is, provide a Clone implementation given that in stratisd, we have a DmError that is part of a lazy_static expression so we cannot move it. It would be preferable to be able to clone it rather that stringifying it and wrapping it as a message.

[jbaublitz]

@mulkieran Please take a look at rust-lang-deprecated/error-chain#134. It appears that we cannot implement Clone for DmError. How would you like me to proceed?

[mulkieran]

@jbaublitz When you have a chance, look into seeing if we can just drop our dependency on error_chain in devicemapper entirely, as I believe that would solve the problem. But this obstacle should not block stratis-storage/stratisd#2667.

[mulkieran]

So, dropping dependency on error_chain is not so hard, but std::io::Error is not cloneable. Also, I'ld like to drop fn description implementation for outer error, see #657. So, might as well defer until after next release.