Reorganize Python packages

This is in preparation of moving all tests into a separate package to
enable ease of coverage checking and testing.
diff --git a/tools/run_tests/build_python.sh b/tools/run_tests/build_python.sh
index ae0fb42..265a542 100755
--- a/tools/run_tests/build_python.sh
+++ b/tools/run_tests/build_python.sh
@@ -43,8 +43,8 @@
     virtualenv -p `which "python"$1` $virtualenv_name
     source $virtualenv_name/bin/activate
     pip install -r src/python/requirements.txt
-    CFLAGS="-I$root/include -std=c89" LDFLAGS=-L$root/libs/$CONFIG GRPC_PYTHON_BUILD_WITH_CYTHON=1 pip install src/python/src
-    pip install src/python/interop
+    CFLAGS="-I$root/include -std=c89" LDFLAGS=-L$root/libs/$CONFIG GRPC_PYTHON_BUILD_WITH_CYTHON=1 pip install src/python/grpcio
+    pip install src/python/grpcio_test
   else
     source $virtualenv_name/bin/activate
     # Uninstall and re-install the packages we care about. Don't use
@@ -52,13 +52,13 @@
     # unnecessarily to dependencies. Don't use --no-deps to avoid missing
     # dependency upgrades.
     (yes | pip uninstall grpcio) || true
-    (yes | pip uninstall interop) || true
-    (CFLAGS="-I$root/include -std=c89" LDFLAGS=-L$root/libs/$CONFIG GRPC_PYTHON_BUILD_WITH_CYTHON=1 pip install src/python/src) || (
+    (yes | pip uninstall grpcio_test) || true
+    (CFLAGS="-I$root/include -std=c89" LDFLAGS=-L$root/libs/$CONFIG GRPC_PYTHON_BUILD_WITH_CYTHON=1 pip install src/python/grpcio) || (
       # Fall back to rebuilding the entire environment
       rm -rf $virtualenv_name
       make_virtualenv $1
     )
-    pip install src/python/interop
+    pip install src/python/grpcio_test
   fi
 }