Make sure the test suite runs from linked directory.

[voxik]

  1) ABRT handles exception in 'abrt.rb' with RubyGems disabled
     Failure/Error:
       expect { system "ruby --disable-gems #{abrt_rb}" }
         .to output(/\A\Z/).to_stdout_from_any_process
         .and output(output_message_pattern).to_stderr_from_any_process
     
       expected block to output /\A\/builddir\/abrt-0.4.0\/spec\/..\/lib\/abrt.rb:\d+:in `<main>': can't modify frozen Array(: \[1, 2, 3\])? \((FrozenError|RuntimeError)\)\n\Z/ to stderr, but output "/usr/bin/ruby-mri: No such file or directory -- /builddir/abrt-0.4.0/spec/../lib/abrt.rb (LoadError)\n"
     # ./spec/abrt_spec.rb:9:in `block (3 levels) in <top (required)>'

  2) ABRT handles exception in 'abrt.rb' with RubyGems enabled
     Failure/Error:
       expect { system "ruby --disable-gems -rrubygems #{abrt_rb}" }
         .to output(/\A\Z/).to_stdout_from_any_process
         .and output(output_message_pattern).to_stderr_from_any_process
     
       expected block to output /\A\/builddir\/abrt-0.4.0\/spec\/..\/lib\/abrt.rb:\d+:in `<main>': can't modify frozen Array(: \[1, 2, 3\])? \((FrozenError|RuntimeError)\)\n\Z/ to stderr, but output "/usr/bin/ruby-mri: No such file or directory -- /builddir/abrt-0.4.0/spec/../lib/abrt.rb (LoadError)\n"
     # ./spec/abrt_spec.rb:15:in `block (3 levels) in <top (required)>'