Split server unit test on its own

Ref https://github.com/sbt/sbt/issues/4186
This is an attempt to fix the flaky server test issue.

.travis.yml

@@ -50,7 +50,7 @@ notifications:
 
 # Undo _JAVA_OPTIONS environment variable
 before_script:
-  - _JAVA_OPTIONS=
+  - unset _JAVA_OPTIONS
 
 script:
   # It doesn't need that much memory because compile and run are forked

build.sbt

@@ -726,20 +726,12 @@ lazy val docProjects: ScopeFilter = ScopeFilter(
 )
 lazy val safeUnitTests = taskKey[Unit]("Known working tests (for both 2.10 and 2.11)")
 lazy val safeProjects: ScopeFilter = ScopeFilter(
-  inProjects(mainSettingsProj, mainProj, actionsProj, runProj, stdTaskProj),
+  inAnyProject -- inProjects(sbtRoot, sbtProj),
   inConfigurations(Test)
 )
 lazy val otherUnitTests = taskKey[Unit]("Unit test other projects")
 lazy val otherProjects: ScopeFilter = ScopeFilter(
   inProjects(
-    testingProj,
-    testAgentProj,
-    taskProj,
-    scriptedSbtProj,
-    scriptedPluginProj,
-    commandProj,
-    mainSettingsProj,
-    mainProj,
     sbtProj
   ),
   inConfigurations(Test)