KotlinBuilder: don't request additional round when it's unnecessary & fix warnings

jps-plugin/testData/incremental/withJava/kotlinUsedInJava/packageFileAdded/build.log

@@ -18,7 +18,5 @@ End of files
 Compiling files:
   src/a.kt
 End of files
-Exit code: ADDITIONAL_PASS_REQUIRED
-------------------------------------------
-Exit code: NOTHING_DONE
+Exit code: OK
 ------------------------------------------

jps-plugin/testData/incremental/withJava/kotlinUsedInJava/packageFileAdded/experimental-ic-build.log

@@ -6,10 +6,8 @@ End of files
 Compiling files:
   src/b.kt
 End of files
-Exit code: ADDITIONAL_PASS_REQUIRED
+Exit code: OK
 ------------------------------------------
 Compiling files:
   src/Usage.java
 End of files
-Exit code: NOTHING_DONE
-------------------------------------------