dma(8): install default conf files with installworld

dma(8): install default conf files with installworld

Previously dma configure files were only installed with the
"make distribution" command.  Additionally, the user was expected to
modify them as opposed to copies of them.  This is probably why there
were part of distribution, in order to avoid overwriting the dma.conf
and auth.conf.

The negative side to this approach is that updated *.conf sample files
would never be installed.  Since the dma.conf is actually completely
commented out, and since it doesn't fail in the absence of dma.conf,
these files aren't actually needed.

This commit installs /etc/dma/dma.conf.sample and /etc/dma/auth.conf.sample
files during installworld instead.  Future updates to the *.conf.sample
files will overwrite them, but obviously /etc/dma/*.conf will not be
touched. Some of the sendfile conf files are provided as .sample, so the
concept is not new for DragonFly.