unbundle: move most of the logic on cmdutil to help debug::unbundle reuse
This make sure `hg debug::unbundle` focus on the core logic.
Test admin::verify
$ hg init admin-verify
$ cd admin-verify
Test normal output
$ hg admin::verify -c dirstate
running 1 checks
running working-copy.dirstate
checking dirstate
Quiet works
$ hg admin::verify -c dirstate --quiet
Test no check no options
$ hg admin::verify
abort: `checks` required
[255]
Test single check without options
$ hg admin::verify -c working-copy.dirstate
running 1 checks
running working-copy.dirstate
checking dirstate
Test single check (alias) without options
$ hg admin::verify -c dirstate
running 1 checks
running working-copy.dirstate
checking dirstate
Test wrong check name without options
$ hg admin::verify -c working-copy.dir
abort: unknown check working-copy.dir
(did you mean working-copy.dirstate?)
[10]
Test wrong alias without options
$ hg admin::verify -c dir
abort: unknown check dir
[10]