With a synced folder configuration like so:
synced_folder ".", "/vagrant", :nfs => true
synced_folder "#{ENV['HOME']}/mirror", "/mirror", :nfs => true
synced_folder ENV['HOME'], "/home/#{ENV['USER']}", :nfs => true
on OSX, vagrant writes two overlapping exports to /etc/exports
which then fail the export check.
Iterating through the list of folders lexically builds a correct, single
exports entry.
Signed-off-by: Teemu Matilainen <teemu.matilainen@iki.fi>