Clone the API key info into all help messages
    
    I was looking at the help text for request-branch and completely
    overlooked the instruction to have a look at request-repo. To imporve
    this, I used a couple of strings and cloned the text into all affected
    commands.
    
    Also fixed some explicit fedpkg mentions with string interpolation in
    the parts I touched.
    
    Merges: https://pagure.io/fedpkg/pull-request/609
    
    Signed-off-by: Michal Pospíšil <mpospisi@redhat.com>