server/rpc: bricks goes offline and comes back online, with lots of "No such file or directory" log messages

Problem:
Messages were getting logged very frequently at log level INFO.

[2013-03-01 11:34:28.029222] I [server3_1-fops.c:1541:server_open_cbk] vol-server: 993888: OPEN (null) (--) ==> -1 (No such file or directory)
[2013-03-01 11:34:28.031579] I [server3_1-fops.c:252:server_inodelk_cbk] vol-server: 993896: INODELK (null) (--) ==> -1 (No such file or directory)
[2013-03-01 11:34:28.034041] I [server3_1-fops.c:252:server_inodelk_cbk] vol-server: 993914: INODELK (null) (--) ==> -1 (No such file or directory)
[2013-03-01 11:34:28.040435] I [server3_1-fops.c:1338:server_flush_cbk] vol-server: 993938: FLUSH -2 (--) ==> -1 (No such file or directory)

Solution:
Moved them to DEBUG log level if error number equlas to ENOENT else to ERROR log level.
It will help in decreasing the size of log files at INFO log level.
For server_open_cbk and for some other functions we already have a patch, below is the URL for it.
URL- http://review.gluster.org/6241
This patch solves logging problem for functions server_inodelk_cbk and server_flush_cbk.

Change-Id: I57372e851371e466f1674726015e28378b826f5f
BUG: 1029372
Signed-off-by: Vikhyat Umrao<vumrao@redhat.com>
Reviewed-on: http://review.gluster.org/6252
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>