Add -k flag to bazel test runs

This will ensure that the build keeps going even if there is an error,
so that we can see as many results as possible without having to fix the
error and kick off another run.

kokoro/linux/bazel/build.sh

@@ -23,7 +23,7 @@ cd $(dirname $0)/../../..
 git submodule update --init --recursive
 
 trap print_test_logs EXIT
-bazel test --copt=-Werror --host_copt=-Werror \
+bazel test -k --copt=-Werror --host_copt=-Werror \
   //:build_files_updated_unittest \
   //java:tests \
   //:protoc \