ruby: install required files for ptest

ruby: install required files for ptest

After update to 2.7.0, it fails to start ptest of ruby with errors:

| ./test/runner.rb:11:in `require_relative': cannot load such file --
    /usr/lib64/ruby/ptest/tool/test/runner (LoadError)

and

| test/rdoc/test_rdoc_attr.rb: cannot load such file -- rdoc/version
| test/did_you_mean/spell_checking/test_key_name_check.rb: cannot load
    such file -- /usr/lib64/ruby/ptest/lib/did_you_mean

Install the required files for the ptest.

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>