`orc update` should force sync binary-archives to remote HEAD

[fcremo]

Currently orc update discards local changes to binary archives before pulling, but expects the remote repositories to not have been force pushed.
This is a reasonable safety measure for source repositories, but unfortunate for binary archives.
Then updating those, orchestra should:

• git clean
• git fetch
• GIT_LFS_SKIP_SMUDGE=1 git reset --hard origin/master