IB/iser: Move informational messages from error to info level

Introduce iser_info() and move informational messages that were
printed as errors to use that macro. Also, cleanup printk leftovers to
use the existing macros.

Signed-off-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
[ Use pr_warn(... instead of printk(KERN_WARNING ....  - Roland ]

Signed-off-by: Roland Dreier <roland@purestorage.com>