console: handle escape character specification

[brauner]

Currently the console code assumes that the escape character can be simply specified as a rune/char passed into the corresponding C function. But actually lxc_console() assumes that 1 == 'a', 2 == 'b' so you need something similar to this C function in go-lxc:

inline char etoc(const char c)
{
	/* returns "control code" of given expression */
	return 1 + ((c > 'Z') ? (c - 'a') : (c - 'Z'));
}

[restototicoserra]

inline char etoc(const char c)
{
/* returns "control code" of given expression */
return 120 + ((c > 'Z') ? (c - 'a') : (c - 'Z'));
}