common: Change way master, chunkserver and metalogger output data

Make it more user-friendly
Messages printed to stderr now have a prefix based on their importance:
[ OK ] - execution successful
[....] - attempting execution
[WARN] - some kind of problem encountered, but it can be managed
[FAIL] - error encountered and it cannot be managed

This commit just changes the implementation of mfs_*log functions to
include these prefixes and renames them to lzfs_*log. Some messages will
be improved in forthcoming commits.

Change-Id: I09f167a679df65985c6ff215cdcdbdb8c7542402
master, chunkserver, metarestore: Improve startup messages

This commit improves most of the messages printed on startup to make it
more clear what the user should do when something goes wrong, e.g.:

  init: hdd space manager failed !!!

is changed to:

  [FAIL] can't open hdd config file /etc/mfs/mfshdd.cfg: ENOENT (No such file or directory) - new file can be created using /etc/mfs/mfshdd.cfg.dist

Change-Id: Iaeffbbabf1a7f322f29e416e7101ab909b3ba8ff