Fix ensureRuby method to be able to switch versions

	- Remove 'git clone' block, because it's not needed
	- Always install to Workspace and not global file path

Related: PROD-26476 (PROD:26476)

Change-Id: I623f9ccf954f3de3d0978671058f953e51167758
diff --git a/src/com/mirantis/mk/Ruby.groovy b/src/com/mirantis/mk/Ruby.groovy
index 32b595e..7802a11 100644
--- a/src/com/mirantis/mk/Ruby.groovy
+++ b/src/com/mirantis/mk/Ruby.groovy
@@ -9,20 +9,13 @@
  * @param rubyVersion target ruby version (optional, default 2.2.3)
  */
 def ensureRubyEnv(rubyVersion="2.4.1"){
-    def ruby_build_root = "~/.rbenv/plugins/ruby-build"
+    def ruby_build_root = "${env.WORKSPACE}/.rbenv/plugins/ruby-build"
     if (!fileExists("/var/lib/jenkins/.rbenv/versions/${rubyVersion}/bin/ruby")){
         //XXX: patch ruby-build because debian package is quite old
-        // Check if git repo exists
-        if (!fileExists("${ruby_build_root}/.git")) {
-            sh "git clone https://github.com/rbenv/ruby-build.git ${ruby_build_root}"
-        } else {
-            // Ensure the repo is up-to-date
-            sh "cd ${ruby_build_root}"
-            sh "git pull"
-        }
-        sh "rbenv install ${rubyVersion}";
+        sh "rbenv install ${rubyVersion} -sv";
     }
     sh "rbenv local ${rubyVersion};rbenv exec gem update --system"
+    sh "rm -rf ${ruby_build_root}"
 }
 
 /**