[BUG] navpgdump crashes with TypeError on Python 3 if exclusion options are provided

[lunkwill42]

Describe the bug

The navpgdump command does not work on Python 3 when invoked with any exclusion argument.

To Reproduce
Steps to reproduce the behavior:

1. Run e.g. navpgdump --only-open-arp
2. See error

Expected behavior

A proper dump should be produced, without errors.

Environment (please complete the following information):

• NAV version installed: 5.0.2

Traceback

Traceback (most recent call last):
  File "/usr/bin/navpgdump", line 3, in <module>
    main()
  File "/opt/venvs/nav/lib/python3.5/site-packages/nav/pgdump.py", line 46, in main
    excluded = set(opts.exclude + opts.filters.keys())
TypeError: can only concatenate list (not "dict_keys") to list