Mount working folder as relative path in /data and respect gitignore.

I modified bdsync to sync into `/data` folder of host, using relative paths not full `pwd`.  I also added `--exclude-from=.gitignore`.  You do need to add .git to your .gitignore, so there's not 1-1 compatibility. but it works pretty well.  This does prevent things like `node_modules` from overwriting with wrong binaries.