Add impl std::error::Error for Error types of vm-vcpu

[cecton]

I just copied the doc comment and added : {0} where possible.

New set of dependencies added:

proc-macro2 pulled by: thiserror-impl
proc-macro2 +proc-macro pulled by: quote, syn
quote pulled by: proc-macro2, thiserror-impl
quote +proc-macro pulled by: syn
syn pulled by: thiserror-impl
thiserror pulled by: vm-vcpu
thiserror-impl pulled by: thiserror
unicode-xid pulled by: proc-macro2, syn

(This can be obtain with my wonderful tool cargo-new-deps :grin: (with colors in terminal :sparkles:))

[andreeaflorescu]

@cecton can you update your PR to fix the arm failures? There are missing implementation on arm which is causing the build to fail.

The commit message needs updating as well. Can you shorten the summary, and also please add in the commit description why is this change needed.

[cecton]

@andreeaflorescu done! My regex failed me xD

[andreeaflorescu]

@cecton the tests on arm are still failing, can you check the error message?