keyctl: use printstr_ex for printing out buffer
keyctl: use printstr_ex for printing out buffer

keyctl_read_key had subtle bug by treating out buffer in KEYCTL_READ
as NUL-terminated, which is not true.  We fix it by adding parameter to
keyctl_read_key signalising whether buffer is NUL-terminated and using
printstr_ex for printing (expectedly) NUL-terminated strings.

* keyctl.c (keyctl_read_key): Add has_nul parameter.  Do not use -1 as
string len.  Use printstr_ex for buffer output with user style depending
on has_nul value.
(SYS_FUNC(keyctl)): Specify has_nul parameter to keyctl_read_key
by comparing cmd value with KEYCTL_READ.

cuviper/strace,cuviper/strace,cuviper/strace,cuviper/strace,cuviper/strace