samples: Minor fixes for bundle

1. Rearrange tasks for C++ and Kotlin compilation in concurrent
sample. It allows the build to download all dependencies before
the compilation.

2. Don't copy *.kt.bc-build directories in the distribution archive.

build.gradle

@@ -397,6 +397,7 @@ task bundle(type: Tar) {
         exclude '**/settings.gradle'
         exclude '**/build'
         exclude '**/.gradle'
+        exclude 'samples/**/*.kt.bc-build'
         rename('(.*)\\.for_bundle', '$1')
         into baseName
     }