Support the integration tests in MiMa

[dwijnand]

Running IntegrationTest/test in fails, while it passes with the regular sbt launcher:

[error] java.util.NoSuchElementException: key not found: (org.scala-lang:scala-library,2.10.0)
[error] 	at scala.collection.immutable.Map$Map1.apply(Map.scala:114)
[error] 	at lmcoursier.internal.SbtUpdateReport$.$anonfun$apply$1(SbtUpdateReport.scala:254)
[error] 	at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:237)
[error] 	at scala.collection.immutable.HashMap$HashMap1.foreach(HashMap.scala:234)
[error] 	at scala.collection.immutable.HashMap$HashTrieMap.foreach(HashMap.scala:465)
[error] 	at scala.collection.TraversableLike.map(TraversableLike.scala:237)
[error] 	at scala.collection.TraversableLike.map$(TraversableLike.scala:230)
[error] 	at scala.collection.AbstractTraversable.map(Traversable.scala:108)
[error] 	at lmcoursier.internal.SbtUpdateReport$.apply(SbtUpdateReport.scala:231)
[error] 	at lmcoursier.internal.UpdateRun$.update(UpdateRun.scala:94)
[error] 	at lmcoursier.CoursierDependencyResolution.$anonfun$update$30(CoursierDependencyResolution.scala:192)
[error] 	at scala.util.Either.map(Either.scala:353)
[error] 	at lmcoursier.CoursierDependencyResolution.$anonfun$update$29(CoursierDependencyResolution.scala:189)
[error] 	at scala.util.Either.flatMap(Either.scala:341)
[error] 	at lmcoursier.CoursierDependencyResolution.update(CoursierDependencyResolution.scala:187)
[error] 	at sbt.librarymanagement.DependencyResolution.update(DependencyResolution.scala:56)
[error] 	at mimabuild.TestsPlugin$.getArtifact(TestsPlugin.scala:166)
[error] 	at mimabuild.TestsPlugin$.$anonfun$runIntegrationTest$1(TestsPlugin.scala:58)
[error] 	at mimabuild.TestsPlugin$.$anonfun$runIntegrationTest$1$adapted(TestsPlugin.scala:52)