add flags param to perlbrew::perl

The flags param defaults to including the `--notest` flag which should
dramatically shorten the time required to install a new perl version.

+ greatly improved test coverage of perlbrew::perl
add timeout param to perlbrew::perl

This change also shortens the default timeout on a perl install from
3600s -> 900s.
Merge pull request #2 from jhoblitt/feature/perlbrew_perl_params

Feature/perlbrew perl params