Add libxml2-utils for `xmllint` tool for repopatch.sh script

Change-Id: Ic80710524603e93f599e2f3a73153c6a9270ae76
diff --git a/packer/provision/basebuild.sh b/packer/provision/basebuild.sh
index 8aa89f0..ff12b60 100644
--- a/packer/provision/basebuild.sh
+++ b/packer/provision/basebuild.sh
@@ -55,6 +55,7 @@
         curl \
         git \
         less \
+        libxml2-utils \
         nodejs \
         npm \
         python \