Do not set entrypoint to Bazel. (#87)

* Do not set entrypoint to Bazel.

Initially, we set entrypoint to bazel to mimic GCB's behavior. But our
use case actually does not need it by default.

Also fix cmd error introduced in the base image.
diff --git a/container/ubuntu16_04/builders/bazel/BUILD b/container/ubuntu16_04/builders/bazel/BUILD
index 5981d30..26460bb 100644
--- a/container/ubuntu16_04/builders/bazel/BUILD
+++ b/container/ubuntu16_04/builders/bazel/BUILD
@@ -18,15 +18,16 @@
 
 load("//container/rules:docker_toolchains.bzl", "toolchain_container")
 load("@io_bazel_rules_docker//contrib:test.bzl", "container_test")
-load(
-    "@io_bazel_rules_docker//container:container.bzl",
-    "container_image",
-)
 
 # Install deb packages.
 toolchain_container(
-    name = "bazel_with_debs",
+    name = "bazel",
     base = "@ubuntu16_04//image",
+    cmd = [
+        "/bin/sh",
+        "-c",
+        "/bin/bash",
+    ],
     # TODO(xingao) Fix this. We should not remove /etc/ssl/certs/java/cacerts
     # file in the java-ltl, but instead, archive it for future container
     # reproduction.
@@ -40,14 +41,6 @@
     ],
 )
 
-# Setup other information, e.g. entrypoint.
-# TODO(xingao): set entrypoint in toolchain_container once supported.
-container_image(
-    name = "bazel",
-    base = ":bazel_with_debs",
-    entrypoint = ["bazel"],
-)
-
 container_test(
     name = "bazel-test",
     configs = [
@@ -64,21 +57,18 @@
 
 # Install deb packages.
 toolchain_container(
-    name = "bazel_docker_with_debs",
-    base = ":bazel_with_debs.tar",
+    name = "bazel_docker",
+    base = ":bazel.tar",
+    cmd = [
+        "/bin/sh",
+        "-c",
+        "/bin/bash",
+    ],
     language_layers = [
         "//container/ubuntu16_04/layers/docker-17.12.0:docker-ltl",
     ],
 )
 
-# Setup other information, e.g. entrypoint.
-# TODO(xingao): set entrypoint in toolchain_container once supported.
-container_image(
-    name = "bazel_docker",
-    base = ":bazel_docker_with_debs",
-    entrypoint = ["bazel"],
-)
-
 container_test(
     name = "bazel_docker-test",
     configs = [
diff --git a/container/ubuntu16_04/builders/bazel/container.yaml b/container/ubuntu16_04/builders/bazel/container.yaml
index 791f95f..a6b95d4 100644
--- a/container/ubuntu16_04/builders/bazel/container.yaml
+++ b/container/ubuntu16_04/builders/bazel/container.yaml
@@ -23,4 +23,3 @@
   env:
     - key: 'PATH'
       value: '/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/opt/python3.6/bin'
-  entrypoint: ['bazel']