title: Gradle dependsOn non gradle project
body: <p>I have a number of gradle projects with a multi-project build stucture.</p>
  
  <p>I use gradle build cache on our buildserver to only run tests in projects with changes or projects which dependsOn projects with changes. This works great and saves a lot of build time.</p>
  
  <p>The problem is:
  Gradle projectA depends on a non gradle projectB, and I don't know how to set this dependency.
  projectB produces a docker used by projectA, and if an error is introduced in projectB, the tests in projectA doesn't run and the error goes into production.</p>
  
  <p>So the question is how do you make a gradle "dependsOn" for any change in a non gradle project.</p>