init: first stage init tie stdout and stderr to /dev/kmsg

It is exceedingly difficult to debug I/O and filesystem corruption
issues during first and selinux initialization stage init.  By
redirecting stderr, and for good measure stdout, to /dev/kmsg in
first stage init before it exec's "/system/bin/init" we can see
the filesystem corruption errors more clearly.

Before this we would see:

init: Skipped setting INIT_AVB_VERSION (not in recovery mode)
Kernel panic - not syncing: Attempted to kill init! exitcode=0x...

and then wonder why?

After this change we can see:

init: Skipped setting INIT_AVB_VERSION (not in recovery mode)
libc: Fatal signal 5 (SIGTRAP), code 128 (SI_KERNEL), fault addr...
Kernel panic - not syncing: Attempted to kill init! exitcode=0x...

-or-

init: Skipped setting INIT_AVB_VERSION (not in recovery mode)
linker: CANNOT LINK EXECUTABLE "/system/bin/init": cannot locate symbol...
Kernel panic - not syncing: Attempted to kill init! exitcode=0x...

(NB: with stutter removed because of stdout and stderr)

Silence from these sources otherwise on successful execution.

Test: boot
Bug: 138459777
Change-Id: I4200b24baeaa6e408a5e0a2c890561bda1e2f1f4