Consider:
When I create a simple Maven project in Eclipse I am getting this error:
web.xml is missing and
You can also do this which is less verbose
<properties>
<failOnMissingWebXml>false</failOnMissingWebXml>
</properties>
If you already have web.xml under /src/main/webapp/WEB-INF but you still get error "web.xml is missing and is set to true", you could check if you have included /src/main/webapp in your project source.
Here are the steps you can follow:
(I verified this with Eclipse Mars)