(PUP-2571) add 'before' functionality to file_line

[stbenjam]

file_line supports adding lines after a match, but there are use cases when
having "before" would be useful. For example, in Debian-based OS's, the last
line of /etc/rc.local is "exit 0" it's an incredible pain to deal with
that scenario today.

This commit adds a 'before' parameter to the file_line type, and implements
it for the ruby provider.

[apenney]

#257 <-- I just had to revert this, it causes puppetlabs-apache tests to fail with:

2. apache::mod::proxy_html on a FreeBSD OS should compile the catalogue without cycles
   Failure/Error: it { should compile.with_all_deps }
   NoMethodError:
   undefined method `to_edges' for #Puppet::Type::File_line::ParameterBefore:0x7fe07e3e1b90

[apenney]

We saw this on Puppet 2.7, so its probably just an issue there.

[stbenjam]

@apenney Oops, sorry about that! I didn't even realize this, but "before" is a bad name because of resource ordering. That's what's breaking puppetlabs-apache (and probably a bunch of other things).

Renaming this to 'precede' fixes the puppetlabs-apache tests. I'm not sure I like "precede" though :-(

I'd rather the structure be something like this with positon being before, after, or overwrite. That's too big of a change I guess.

file_line { "nisdomain_live":
  path     => '/etc/rc.local',
  match    => '^exit 0$',
  position => before, 
}