Redirect libselinux logging to dmesg for ueventd.

We already do this for init, but had failed to do it for ueventd
and could not capture any logging from libselinux calls made by
ueventd.

Truly enabling non-error logging also requires uncommenting a line
in Android.mk:
LOCAL_CFLAGS += -DLOG_UEVENTS=1
which enables other logging and sets the default log level to INFO,
or otherwise changing the klog level in the ueventd code (is not
settable by init.rc loglevel).

Change-Id: I00e6f9d6271f2a21d9078c96368816d74d6d2850
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>