sulogin: start _login_ shell only with -p

Also, shorten/eliminate messages to be closer to util-linux.

function                                             old     new   delta
packed_usage                                       34233   34238      +5
sulogin_main                                         340     341      +1
.rodata                                           104380  104327     -53
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/1 up/down: 6/-53)             Total: -47 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
1 file changed