include man in el8

[kpedro88]

Currently, in cmssw-el8, a command like git cms-rebase-topic --help produces the following error:

warning: failed to exec 'man': No such file or directory
fatal: no man viewer handled the request

man is provided by the rpm man-db. Since cmssw-el8 is commonly being used for interactive development now, it should be included.

[cmsbuild]

A new Pull Request was created by @kpedro88 (Kevin Pedro) for branch master.

@cmsbuild, @smuzaffar, @aandvalenzuela, @iarspider can you please review it and eventually sign? Thanks. @perrotta, @dpiparo, @qliphy, @rappoccio you are the release manager for this. cms-bot commands are listed here

[smuzaffar]

@kpedro88 , new container with the change should be available tomorrow afternoon