Add ability to clean peppervenv

Currently by default pepper will use old venv
with old token which can expire.

This commit adds ability to specify venv clean flag,
but keeps default behavior the same - not do cleaning.

Change-Id: I916888b66a71a086aa39fc4f568bb1ca4bcbb65b
Related-Prod: https://mirantis.jira.com/browse/PROD-16019
diff --git a/src/com/mirantis/mk/Python.groovy b/src/com/mirantis/mk/Python.groovy
index c746ef2..b6e408a 100644
--- a/src/com/mirantis/mk/Python.groovy
+++ b/src/com/mirantis/mk/Python.groovy
@@ -298,14 +298,14 @@
  * @param url         SALT_MASTER_URL
  * @param credentialsId        Credentials to salt api
  */
-def setupPepperVirtualenv(path, url, credentialsId) {
+def setupPepperVirtualenv(path, url, credentialsId, clean = false) {
     def common = new com.mirantis.mk.Common()
 
     // virtualenv setup
     // TODO: once pepper changes are in pypi, reenable these lines
     // requirements = ['salt-pepper']
     requirements = []
-    setupVirtualenv(path, 'python2', requirements, null, false, true)
+    setupVirtualenv(path, 'python2', requirements, null, clean, true)
     runVirtualenvCommand(path, "pip install git+https://github.com/chnyda/pepper.git")
 
     // pepperrc creation