base: kernel logging get pre-opened /dev/kmsg from environment

If the environment has an instance of /dev/kmsg pre-opened, pick up.
This happens when an init script has 'file w /dev/kmsg' in the
daemon's recipe.

libcutils android_get_control_file operations are open-coded to
prevent a dependency on libcutils itself.  Also check that /dev/kmsg
file descriptor is valid and open'd for write only.

Test: check to make sure init() kernel logging still works
Bug: 77541952
Bug: 77661605
Change-Id: I007553acd594ef0815d23f32f8aa2867518570ba