BUG/MEDIUM: logs: segfault writing to log from Lua

Michael Ezzell reported a bug causing haproxy to segfault during startup
when trying to send syslog message from Lua. The function __send_log() can
be called with *p that is NULL and/or when the configuration is not fully
parsed, as is the case with Lua.

This patch fixes this problem by using individual vectors instead of the
pre-generated strings log_htp and log_htp_rfc5424.

Also, this patch fixes a problem causing haproxy to write the wrong pid in
the logs -- the log_htp(_rfc5424) strings were generated at the haproxy
start, but "pid" value would be changed after haproxy is started in
daemon/systemd mode.
diff --git a/include/types/log.h b/include/types/log.h
index 411ba8f..35c1228 100644
--- a/include/types/log.h
+++ b/include/types/log.h
@@ -30,7 +30,7 @@
 
 #define NB_LOG_FACILITIES       24
 #define NB_LOG_LEVELS           8
-#define NB_MSG_IOVEC_ELEMENTS   5
+#define NB_MSG_IOVEC_ELEMENTS   8
 #define SYSLOG_PORT             514
 #define UNIQUEID_LEN            128