Unfriendly response to command line typo

If you mis-type an app id on the command line, you get a traceback and exception message. The correct output is already there, but it's lost amongst the rest. Example:

~/ciarangrepo$ fdroid build -l --test com.type
No such package: com.typo
Traceback (most recent call last):
  File "/home/ciaran/fdroidserver/fdroid", line 87, in <module>
    main()
  File "/home/ciaran/fdroidserver/fdroid", line 83, in main
    mod.main()
  File "/home/ciaran/fdroidserver/fdroidserver/build.py", line 924, in main
    apps = common.read_app_args(args, allapps, True)
  File "/home/ciaran/fdroidserver/fdroidserver/common.py", line 178, in read_app_args
    raise Exception("Found invalid app ids in arguments")
Exception: Found invalid app ids in arguments

Clearly the actual output should be just the first line, "No such package..."