nuxeo.webui.mp.version should be updated during the platform release prepare step

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <parent>
    <groupId>org.nuxeo</groupId>
    <artifactId>nuxeo-addons-parent</artifactId>
    <version>9.10-I20171217_2311</version>
    <relativePath>../addons/pom.xml</relativePath>
  </parent>

  <groupId>org.nuxeo.ecm.distribution</groupId>
  <artifactId>nuxeo-distribution</artifactId>
  <packaging>pom</packaging>
  <name>Nuxeo Distribution Parent</name>
  <description>Build package distributions of nuxeo applications</description>

  <prerequisites>
    <maven>3.1.1</maven>
  </prerequisites>

  <properties>
    <nuxeo.distribution.version>9.10-I20171217_2311</nuxeo.distribution.version>
    <nuxeo.webui.mp.version>2.2.0-SNAPSHOT</nuxeo.webui.mp.version>
  </properties>