Ruby linux testing support

test/distrib/ruby/run_distrib_test.sh

tools/dockerfile/distribtest/ruby_centos6_x64/Dockerfile

tools/dockerfile/distribtest/ruby_centos7_x64/Dockerfile

tools/dockerfile/distribtest/ruby_fedora20_x64/Dockerfile

tools/dockerfile/distribtest/ruby_fedora21_x64/Dockerfile

tools/dockerfile/distribtest/ruby_fedora22_x64/Dockerfile

tools/dockerfile/distribtest/ruby_fedora23_x64/Dockerfile

tools/dockerfile/distribtest/ruby_jessie_x64/Dockerfile

tools/dockerfile/distribtest/ruby_jessie_x86/Dockerfile

tools/dockerfile/distribtest/ruby_opensuse_x64/Dockerfile

tools/dockerfile/distribtest/ruby_ubuntu1204_x64/Dockerfile

tools/dockerfile/distribtest/ruby_ubuntu1404_x64/Dockerfile

tools/dockerfile/distribtest/ruby_ubuntu1504_x64/Dockerfile

tools/dockerfile/distribtest/ruby_ubuntu1510_x64/Dockerfile

tools/dockerfile/distribtest/ruby_ubuntu1604_x64/Dockerfile

tools/dockerfile/distribtest/ruby_wheezy_x64/Dockerfile

tools/run_tests/distribtest_targets.py