main: Copy cmd line args and print them

This makes it really easy to spot on what arguments have been passed to
the compositor. When a test client will run the compositor this will be
helpful to verify that we pass the correct arguments.

Fixes a small typo along the way.

Bug-AGL: SPEC-3880

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
Change-Id: Ia4198ce6bff465f479cf9a0a87c17998c5548868