erlxc_drv: avoid using a shell

To prevent issues with shell metacharacters, invoke the erlxc binary
using exec/argv.

For consistency, do the same with erlxc_console but note that, since
script runs the arguments to -c using bash, any metacharacters will
still be expanded. There are 2 ways to minimize accidents with
metacharacters:

1. Restrict the allowed characters to a whitelist.

hostname: see RFC 952

Valid characters are [a-zA-Z0-9.-]

path: difficult because of UTF encoding of paths

escape: printable ascii (e.g., ctl-% q)

tty: [0-9]

2. Write a plain port that uses the lxccontainer console functions and the
term handling from script command.
'none' -> 'false'