Warn when unable to upgrade keystore on debian (elastic#51011)

For Red Hat RPM upgrades, we warn if we can't upgrade the keystore. This
commit brings the same logic to the code for Debian packages. See the
posttrans file for gets executed for RPMs.

Author: williamrandolph

distribution/packages/src/common/scripts/postinst

@@ -108,7 +108,12 @@ if [ "$PACKAGE" = "deb" ]; then
         chmod 660 "${ES_PATH_CONF}"/elasticsearch.keystore
         md5sum "${ES_PATH_CONF}"/elasticsearch.keystore > "${ES_PATH_CONF}"/.elasticsearch.keystore.initial_md5sum
     else
-        /usr/share/elasticsearch/bin/elasticsearch-keystore upgrade
+        if /usr/share/elasticsearch/bin/elasticsearch-keystore has-passwd --silent ; then
+          echo "### Warning: unable to upgrade encrypted keystore" 1>&2
+          echo " Please run elasticsearch-keystore upgrade and enter password" 1>&2
+        else
+          /usr/share/elasticsearch/bin/elasticsearch-keystore upgrade
+        fi
     fi
 fi