Check for redir before forwarding ports

Make a system call out to `which` to see if redir exists on the PATH
before trying to forward ports.  Raises a VagrantError if it does not.
repair whitespace
Check for redir before booting the machine
stub out call to system
Test coverage for 'check for redir'

Includes a minor refactor allowing variation of the result of the system
call per test
Merge branch 'check-for-redir' of https://github.com/zeroem/vagrant-lxc
Update changelog