When a vagrant box has two private network ips /etc/network/interfaces
will duplicate eth2 and bigger. sed matches greedy, so the first
#VAGRANT-END matches. This will result in:
/etc/network/interfaces:29: interface eth2 declared allow-auto twice
/sbin/ifup: couldn't read interfaces file "/etc/network/interfaces"
When using pty=true, removing files using sudo may request confirmation,
which will hang the connection.
Similarly, sometimes assumptions about file existence may be wrong and
in those cases it seems better to continue on as long as the file does
not exist, so -f makes sense there, too.
