Add methods for Gerrit CR upload

The patch adds git and gerrit methods to
upload CR to Gerrit using pipelines.
Git`s "commitGitChanges" method has been
modified to support "-- amend" option.

Change-Id: I6f61784d0edf956418b033aae2407f1f868d5067
Related-PROD: PROD-30632
diff --git a/src/com/mirantis/mk/Git.groovy b/src/com/mirantis/mk/Git.groovy
index 575fb80..d9006fa 100644
--- a/src/com/mirantis/mk/Git.groovy
+++ b/src/com/mirantis/mk/Git.groovy
@@ -100,13 +100,20 @@
  * @param path            Path to the git repository
  * @param message         A commit message
  * @param global          Use global config
+ * @param amend           Whether to use "--amend" in commit command
  */
-def commitGitChanges(path, message, gitEmail='jenkins@localhost', gitName='jenkins-slave', global=false) {
+def commitGitChanges(path, message, gitEmail='jenkins@localhost', gitName='jenkins-slave', global=false, amend=false) {
     def git_cmd
+    def gitOpts
     def global_arg = ''
     if (global) {
         global_arg = '--global'
     }
+    if (amend) {
+        gitOpts = '--amend'
+    } else {
+        gitOpts = ''
+    }
     dir(path) {
         sh "git config ${global_arg} user.email '${gitEmail}'"
         sh "git config ${global_arg} user.name '${gitName}'"
@@ -116,14 +123,13 @@
             returnStdout: true
         ).trim()
         git_cmd = sh(
-            script: "git commit -m '${message}'",
+            script: "git commit ${gitOpts} -m '${message}'",
             returnStdout: true
         ).trim()
     }
     return git_cmd
 }
 
-
 /**
  * Push git changes to remote repo
  *
@@ -231,4 +237,5 @@
                 returnStdout: true
         ).trim()
     return branchesList.tokenize('\n')
-}
\ No newline at end of file
+}
+