client: make exception more noticeable
client: make exception more noticeable

Exception is not so visible if command is very long.
e.g. https://crbug.com/1198727#c8

Bug: 1198727
Change-Id: I80a0eb9bb2220cc9db36b5e70db5ed4b021c2f93
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-py/+/2825051
Auto-Submit: Takuto Ikuta <71927f930fca81015e0f496c65cd126ab1a692e3@chromium.org>
Commit-Queue: Yoshisato Yanagisawa <5d95c5c75e3d691d9c77888fff4498e04f8b7157@google.com>
Reviewed-by: Yoshisato Yanagisawa <5d95c5c75e3d691d9c77888fff4498e04f8b7157@google.com>
Reviewed-by: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py