Increase early boot logging to kernel log

Make vold log warnings and errors to the kernel log until both
init_user0 has run and /data is mounted.  Previously it only logged
errors, and not warnings, to the kernel log until /data is mounted.

This is helpful to diagnose failures of init_user0, since adb still
isn't started by that point.

Also, error messages can be misleading without seeing related warning
messages, e.g. the following which is expected on many devices:

    E vold    : keystore2 Keystore generateKey returned service specific error: -67
    W vold    : Failed to generate rollback-resistant key.  This is
                expected if keystore doesn't support rollback
                resistance.  Falling back to non-rollback-resistant key.

Therefore, increase the log level to WARNING and above.

Test: Intentionally broke fscrypt_init_user0(), then verified that the
      error and warning messages appear in the kernel log on Cuttlefish.
Bug: 205314634
Bug: 222540970
Change-Id: Ia751f7c88cbf28caf81e891a518953cc0cee911e