add functionality to bool2str function

[mmckinst]

The bool2str function already exists and converts a boolean true/false to a string true/false. It is not documented in the README.

There are cases when something expects a boolean value to be something other than true/false, such as yes/no, t/f, Yes/No, on/off, etc.

This pull request add an optional two element array that bool2str will accept and convert the boolean true/false to the corresponding value in the array. If no array is given, it converts boolean true/false to a string true/false (which also preserves backwards compatibility).

Examples:

bool2str(true)                   => 'true'
bool2str(true, ['yes', 'no'])    => 'yes'
bool2str(false, ['t', 'f'])      => 'f' 

[DavidS]

bool2str is already of questionable value, given that it basically implements $val ? { true => 'true', false => 'false', default => fail("need a bool for val, not '$val'") }.

That said, I would still merge this as it has good docs and tests, if you change the array to two separate parameters. That's another two keystrokes saved.

[mmckinst]

@DavidS I concur on the usefulness of the old bool2str. Hopefully this will make it more useful because there's been plenty of times where I've done something like $val ? 'On' : 'Off' in a template. But now I can convert values right in a manifest and use augeas or file_line to modify files too.

I've updated and squashed my code so it doesn't use an array any more.