cmdline: Use free+strdup instead of realloc+strcpy

cmdline: Use free+strdup instead of realloc+strcpy

The cmdline_set_path function contains logic to reallocate memory of
command path and copy a new value into it.

Inline a simpler free+strdup alternative into __archive_cmdline_parse.
Since the function is always called with empty data, free could be
removed as well. I've kept it that way just to make sure that it's 100 %
compatible with previous code.

Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>