Refactor and cleanup codes. No functional changes.

WORKSPACE

@@ -1,49 +1,62 @@
 workspace(name = "provisioning_sdk")
+load("@bazel_tools//tools/build_defs/repo:git.bzl", "new_git_repository", "git_repository")
+
+# CCTZ (Time-zone framework), needed by abseil.
+git_repository(
+    name = "com_googlesource_code_cctz",
+    remote = "https://github.com/google/cctz.git",
+    tag = "v2.2",
+)
+
+git_repository(
+    name = "abseil_repo",
+    commit = "475d64f2de7403a01b1b36c487328ed41d29c20c",  #2018-04-10
+    remote = "https://github.com/abseil/abseil-cpp.git",
+)
 
 git_repository(
     name = "protobuf_repo",
     remote = "https://github.com/google/protobuf.git",
-    tag = "v3.2.0",
+    tag = "v3.6.1.3",
 )
 
 git_repository(
     name = "boringssl_repo",
-    commit = "bbcaa15b0647816b9a1a9b9e0d209cd6712f0105",  # 2016-07-11
+    commit = "14164f6fef47b7ebd97cdb0cea1624eabd6fe6b8",  # 2018-11-26
     remote = "https://github.com/google/boringssl.git",
 )
 
 git_repository(
     name = "gflags_repo",
-    commit = "fe57e5af4db74ab298523f06d2c43aa895ba9f98",  # 2016-07-20
+    commit = "e171aa2d15ed9eb17054558e0b3a6a413bb01067",  # 2018-11-11
     remote = "https://github.com/gflags/gflags.git",
 )
 
-new_git_repository(
+git_repository(
     name = "googletest_repo",
-    build_file = "gtest.BUILD",
-    commit = "ec44c6c1675c25b9827aacd08c02433cccde7780",  # 2016-07-26
+    commit = "b6cd405286ed8635ece71c72f118e659f4ade3fb",  # 2019-01-04
     remote = "https://github.com/google/googletest.git",
 )
 
 new_git_repository(
     name = "glog_repo",
-    build_file = "glog.BUILD",
+    build_file = "@//:glog.BUILD",
     commit = "0472b91c5defdf90cff7292e3bf7bd86770a9a0a",  # 2016-07-13
     remote = "https://github.com/google/glog.git",
 )
 
 # py_proto_library depends on six indirectly (py_proto_library uses
 # protobuf_python as its default runtime which depends on six).
-new_http_archive(
-    name = "six_archive",
-    build_file = "@protobuf_repo//:six.BUILD",
-    sha256 = "105f8d68616f8248e24bf0e9372ef04d3cc10104f1980f54d57b2ce73a5ad56a",
-    url = "https://pypi.python.org/packages/source/s/six/six-1.10.0.tar.gz#md5=34eed507548117b2ab523ab14b2f8b55",
+new_git_repository(
+    name = "six_repo",
+    build_file = "@//:six.BUILD",
+    remote = "https://github.com/benjaminp/six.git",
+    tag = "1.10.0",
 )
 
 bind(
     name = "six",
-    actual = "@six_archive//:six",
+    actual = "@six_repo//:six",
 )
 
 bind(