Move sbt's testingProj and testAgentProj to this repository

[Duhemm]

There are two projects in sbt that do not depend on other non-extracted sbt component:

// Runner for uniform test interface
lazy val testingProj = (project in file("testing")).
  dependsOn(testAgentProj).
  settings(
    baseSettings,
    name := "Testing",
    libraryDependencies ++= Seq(testInterface, launcherInterface % Compile, ioProj, classpathProj, logProj)
  )

// Testing agent for running tests in a separate process.
lazy val testAgentProj = (project in file("testing") / "agent").
  settings(
    minimalSettings,
    name := "Test Agent",
    libraryDependencies += testInterface
  )

Should we extract them to this repository? There's already a subproject name util-testing in this repository, so it may make sense.

Only project depending on this:

// Implementation and support code for defining actions.
lazy val actionsProj = (project in mainPath / "actions").
  dependsOn (runProj, stdTaskProj, taskProj, testingProj).
  settings(
    testedBaseSettings,
    name := "Actions",
    libraryDependencies ++= Seq(classpathProj, completeProj, apiProj, compilerIntegrationProj, compilerIvyProj,
      interfaceProj, ioProj, ivyProj, logProj, relationProj, trackingProj)
  )

[eed3si9n]

util-testing is an utility for our own unit tests.

testingProj will likely become its own repository as it is an abstraction layer for all testing frameworks.