Show message when worktree is not updated
but Worktree.Pull() returned nil.

e.g.:
upstream remote URL is changed but the repository is identical.
Before: https://github.com/tyru/dummy
After: git@github.com:tyru/dummy.git

"volt get -u" did git-fetch(bare)/git-clone(non-bare) from only remote "origin".
Implemented pulling from upstream remote.

getParallelResult's "status" and "err" have duplicate information.
It is hard to see what's real cause if these information are output twice.

When the config value is true, "volt get" or "volt get -u" fail and
"git" command is installed, it tries to execute "git clone" or
"git pull" as a fallback.

[volt get] When clone/fetch/pull is failed, should try to run git command