use getFileContent as NonCPS

Change-Id: Id83a57a9c8b37ed1b6703619bf3beb6cee0adf5b
diff --git a/src/com/mirantis/mk/Salt.groovy b/src/com/mirantis/mk/Salt.groovy
index 6180f99..e26c931 100644
--- a/src/com/mirantis/mk/Salt.groovy
+++ b/src/com/mirantis/mk/Salt.groovy
@@ -398,6 +398,7 @@
  * @param file      File path to read (/etc/hosts for example)
  */
 
+@NonCPS
 def getFileContent(master, target, file) {
     result = cmdRun(master, target, "cat ${file}")
     return result['return'][0].values()[0]