Fix buildbot master pip installation

PR #132 added service_identity to a pip.installed state which was using
name instead of pkgs because it only had one package to install
(buildbot). Use pkgs instead everywhere and create a style guide.

STYLE_GUIDE.md

@@ -0,0 +1,34 @@
+# Style Guide
+
+Style guide for Salt states (and other code) in this repo. Unfortunately,
+no linter exists yet for Salt states, so there is no automated way to
+check for compliance with this guide.
+
+## Package Installation
+
+### Use pkgs instead of name
+
+pkg.installed, pip.installed, and any other states which install packages
+should use the ```pkgs``` option instead of the ```name``` option to specify
+which package(s) to install, even if there is only one package. This prevents
+problems when adding another package, as in #132 (fixed in #97). Adding another
+name option will cause the earlier option to be silently swallowed, which can
+be hard to debug. Using pkgs from the beginning ensures correct behavior
+regardless of the number of packages.
+
+*Unsafe*:
+
+```salt
+buildbot-dependencies:
+  pip.installed:
+    - name: buildbot == 0.8.12
+```
+
+*Better*:
+
+```salt
+buildbot-dependencies:
+  pip.installed:
+    - pkgs:
+      - buildbot == 0.8.12
+```

buildbot/master.sls

@@ -1,7 +1,8 @@
 buildbot:
   pip.installed:
-    - name: buildbot == 0.8.12
-    - name: service_identity == 14.0.0
+    - pkgs:
+      - buildbot == 0.8.12
+      - service_identity == 14.0.0
 
 txgithub:
   pip.installed
@@ -12,6 +13,8 @@ boto:
 buildbot-master:
   service.running:
     - enable: True
+    - require:
+      - pip: buildbot
 
 /home/servo/buildbot/master:
   file.recurse:

buildbot/slave.sls

@@ -2,7 +2,8 @@
 
 buildbot-slave.pip:
   pip.installed:
-    - name: buildbot-slave == 0.8.12
+    - pkgs:
+      - buildbot-slave == 0.8.12
 
 {{ common.servo_home }}/buildbot/slave:
   file.recurse: