Adjust some Process.uid= specs for 2.0

It looks modified on r35158 for http://bugs.ruby-lang.org/issues/5610.
Adjust some Process.euid= specs for 2.0

It looks modified on r35158 for http://bugs.ruby-lang.org/issues/5610.
Tag failing Process.{uid=,euid=} specs on 2.0
Merge pull request #2537 from kachick/spec-process-uid=,euid=

Adjust some Process.{uid=,euid=} specs for 2.0