soccr: add prefixes for log messages and print errno

loge() will start a message with "Error:" and
logd() will start a message with "Debug:".
logerr() will add strerror(errno) to the end of messages.

travis-ci: success for series starting with [01/21] build: install libnet-dev
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>