main: print parsing errors to stderr
main: print parsing errors to stderr

Use stderr rather than stdout when a parsing error occurs. We can't use
the syslog at this point since it can't be initalized until after args
are parsed, and stderr is more appropriate for error (rather than
informational) messages.

BUG=None
TEST=Ensure crosvm run with errors prints to stderr (2>test.log)

Change-Id: Ifb80c9d72ecd36a2de98b3b3b6f203def1ba7b19
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/3813992
Reviewed-by: Dennis Kempin <cd09796fb571bec2782819dbfd33307f65b1c778@google.com>
Tested-by: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Commit-Queue: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>
Reviewed-by: Noah Gold <2d4550d8af93bfc6e6fbe1fb1b0cc97a9ee7c3ce@google.com>

google/crosvm,google/crosvm,google/crosvm,google/crosvm