get: `get -o` behavior should be consistent with `import -o`

[pmrowla]

As noted in treeverse/dvc.org#1668, get and import behave differently when using -o foo/bar.
import will fail if directory foo/ does not already exist, but get will create the directory.

dvc get should fail instead of using makedirs when foo/ does not exist to behave more consistently with other DVC commands.