pw_env_setup: get Kythe from CIPD

Get Kythe from CIPD. Since Kythe is distributed by source and includes
BUILD files, create .bazelignore and add .cipd to it so we don't try
to build things inside Kythe.

See also https://kythe.io/

Bug: 174
Change-Id: Ied6e03da84a5ce42fc1f8c73af7a18035eafbee3
diff --git a/.bazelignore b/.bazelignore
new file mode 100644
index 0000000..ddee9cb
--- /dev/null
+++ b/.bazelignore
@@ -0,0 +1 @@
+.cipd
diff --git a/pw_env_setup/py/pw_env_setup/cipd_setup/pigweed.json b/pw_env_setup/py/pw_env_setup/cipd_setup/pigweed.json
index 370e115..043d54f 100644
--- a/pw_env_setup/py/pw_env_setup/cipd_setup/pigweed.json
+++ b/pw_env_setup/py/pw_env_setup/cipd_setup/pigweed.json
@@ -105,5 +105,11 @@
     "tags": [
       "git_revision:f3497771a70ba80987c80490aa688794ed971820"
     ]
+  }, 
+  {
+    "path": "pigweed/third_party/kythe", 
+    "tags": [
+      "version:0.0.43"
+    ]
   }
-]
\ No newline at end of file
+]