Fix regexp processing in comparePillars

Change-Id: Id96a2db734bbbcad3561f3b43c69f07ee77159d1
diff --git a/src/com/mirantis/mk/Common.groovy b/src/com/mirantis/mk/Common.groovy
index 570b7a2..9d34d70 100644
--- a/src/com/mirantis/mk/Common.groovy
+++ b/src/com/mirantis/mk/Common.groovy
@@ -634,12 +634,14 @@
     if (diff_status == 1) {
         // Unfortunately, diff not able to work with dir-based regexp
         if (grepOpts) {
-            sh(script: """
+            dir(compRoot) {
+                sh(script: """
                 cp -v pillar.diff pillar_orig.diff
                 grep ${grepOpts} pillar_orig.diff  > pillar.diff
                 """,
-                returnStatus: false
-            )
+                    returnStatus: false
+                )
+            }
         }
         // Analyse output file and prepare array with results
         String data_ = readFile file: "${compRoot}/pillar.diff"