Refactoring test_eu_nest_uid_next_gid due to ruby-2.0.0 bug

    ruby-2.0.0-p451 has a strange bug in rb_ary_push or
    rb_ary_includes that manifests only while testing `#next_uid` and
    `#next_gid` causing a segfault.  ruby-2.0.0-p353 did not show this
    problem.  Running EU.next_uid{,=,()} from the IRB console also was free
    of the issue in either ruby version.

    Not sure if the bug is in Unit/Test or Ruby-Core, so I haven't
    opened an upstream bug.
Updating Travis build tests and adding 2.1.1