filter out duplicates in find_flexlm_license

[boegel]

This is probably enough to fix the regression reported in easybuilders/easybuild-easyblocks#933, but it seems like there's more going on (in IntelBase, that is).

@damianam: you're somewhat familiar with this, please review? ;)

[boegel]

awaiting feedback from @MalkinE to see whether this helps with the reported issue

[MalkinE]

This fixes the mentioned issue. Thanks @boegel!

[damianam]

LGTM. But anybody reading this should probably know that this fix hides a potentially weirder problem (on Intel's side or in particular user configurations, where exactly is not clear) on the installation of intel tools. In particular, exist_lic should work with $INTEL_LICENSE_FILE, without further specifying a license file entry in silent.cfg.

This fix worked in the reported issue because with it we simply avoid setting exist_lic (unnecessarily) in favour of license_server or license_file.

[boegel]

Details on the latter are available at easybuilders/easybuild-easyblocks#933

Thanks for the review @damianam, and @MalkinE for confirming the fix!