Stop using old Ruby versions for test-salt-formula jobs

Use stable 2.6.6 default from pipeline-library

Change-Id: I567bc55563f3d01d676ef6817e7fabc012cb81c6
Related-Prod: PROD-36020
diff --git a/test-salt-formulas-pipeline.groovy b/test-salt-formulas-pipeline.groovy
index 640cfed..2876af1 100644
--- a/test-salt-formulas-pipeline.groovy
+++ b/test-salt-formulas-pipeline.groovy
@@ -188,15 +188,13 @@
               common.infoMsg("Openstack Kitchen test configuration found, running Openstack kitchen tests.")
               kitchenFileName = ".kitchen.openstack.yml"
               envOverrides.add("KITCHEN_YAML=${kitchenFileName}")
-              rubyVersion = '2.5.0'
             } else if (fileExists(".kitchen.yml")) {
               common.infoMsg("Docker Kitchen test configuration found, running Docker kitchen tests.")
               kitchenFileName = ".kitchen.yml"
-              rubyVersion = '2.4.1'
             }
             if (kitchenFileName) {
               def kitchenEnvs = []
-              ruby.ensureRubyEnv(rubyVersion)
+              ruby.ensureRubyEnv()
               if (!fileExists("Gemfile")) {
                 sh("curl -s -o ./Gemfile 'https://gerrit.mcp.mirantis.com/gitweb?p=salt-formulas/salt-formulas-scripts.git;a=blob_plain;f=Gemfile;hb=refs/heads/master'")
                 ruby.installKitchen()