[C++] IWYU docker image silently fails

[asfimport]

ARROW-4528 silently removed iwyu from the list of installed packages. The iwyu_tool.py does not propagate errors correctly if iwyu binary is not found. This seems to be resolved in more recent version, which will be addressed in ARROW-4340.

Reporter: Francois Saint-Jacques / @fsaintjacques

Related issues:

• [C++] Update IWYU version in the lint dockerfile (is duplicated by)

PRs and other links:

• GitHub Pull Request #3638

_{Note: This issue was originally created as ARROW-4564. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
The absence of the include-what-you-use binary is addressed in my patch for ARROW-4340. It would be nice to improve the script to not fail silently