Wizard gives unhelpful error message when install fails

[ezyang]

An example, from installing Wordpress with an empty admin username:

ERROR: Traceback (most recent call last):
  File "/mit/scripts/wizard/bin/wizard", line 128, in main
    command_module.main(rest_argv, baton)
  File "/afs/athena.mit.edu/contrib/scripts/wizard/wizard/command/install.py", line 68, in main
    application.install(v, options)
  File "/afs/athena.mit.edu/contrib/scripts/wizard/wizard/app/wordpress.py", line 116, in install
    raise app.InstallFailure()
InstallFailure: 

ERROR: Installation failed for unknown reason.  You can
retry the installation by appending --retry to the installation
command.

There are a few ways you could go about improving this. The very simplest method is to catch errors in Wizard itself (e.g. assert admin user name is not null); however, this entails code duplication. Another is to parse the HTML output of the script in order to extract information on the error. An easy thing to do is dump the HTML to screen (or provide a temporary link where the error message can be viewed).