packaging: Fix firewalld installation message

The formatting of the message that contains the instructions to enable
firewalld is incorrect, it doesn't contain any parameter but the format
string includes a %s. Also the name is not very descriptive. This patch
fixes both things.

Change-Id: I928f88a188bec11a193c265bc57836f232996b01
Signed-off-by: Juan Hernandez <juan.hernandez@redhat.com>