samples/subsys/pmci/mctp: Make host/endpoint sample messages friendly

This patch achieves that by:
  - Waiting one second between each message sent by the host, so people
    can actually follow what's going on;
  - Wraping the content of the messages (strings "hello" and "world") in
    quotes, so it's clear what they are;
  - Toning down the logging to INF - no need for DBG;
  - Removing astray `\n` - LOG_XXX already takes care of that.

Signed-off-by: Ederson de Souza <ederson.desouza@intel.com>