dib-lint: use yamllint to parse YAML files

This gives us better linting of YAML files that just opening them.
This would have detected the duplicate keys in
I34e27d821fbefe274e7b007f37b0bd34db2e1d26.

The .yamllint is taken from zuul-jobs where it is also used as a
fairly sane set of default rules.

A few minor newline fixes are added.

Change-Id: I96d6644ae24f7deb84fa50fefbda0f0d33e0e009

.yamllint

@@ -0,0 +1,20 @@
+extends: default
+ignore: |
+  .tox
+
+rules:
+  braces:
+    max-spaces-inside: 1
+    level: error
+  brackets:
+    max-spaces-inside: 1
+    level: error
+  document-start: disable
+  empty-lines:
+    max: 1
+    max-end: 2
+  indentation:
+    level: error
+    indent-sequences: consistent
+  line-length: disable
+  truthy: false

bin/dib-lint

@@ -276,17 +276,7 @@ fi
 echo "Checking YAML parsing..."
 for i in $(find $ELEMENTS_DIR -type f -name '*.yaml'); do
     echo "Parsing  $i"
-    py_check="
-import yaml
-import sys
-try:
-    objs = yaml.safe_load(open('$i'))
-except yaml.parser.ParserError:
-    sys.exit(1)
-"
-    if ! python -c "$py_check"; then
-        error "$i is not a valid YAML file"
-    fi
+    yamllint -s -f parsable $i
 done
 echo "Checking pkg-map files..."
 for i in $(find $ELEMENTS_DIR -type f \

diskimage_builder/elements/dib-run-parts/package-installs.yaml

@@ -1 +1 @@
-dib-utils:
+dib-utils:

diskimage_builder/elements/growroot/package-installs.yaml

@@ -1,2 +1,2 @@
 growpart:
-e2fsprogs:
+e2fsprogs:

diskimage_builder/elements/yum-minimal/package-installs.yaml

@@ -17,4 +17,4 @@ linux-firmware-whence:
 # mirrors the default packages installed in upstream cloud images
 # to facilitate a basic network.
 NetworkManager:
-dhcp-client:
+dhcp-client:

test-requirements.txt

@@ -12,3 +12,5 @@ testrepository>=0.0.18 # Apache-2.0/BSD
 testtools>=2.2.0 # MIT
 
 coverage!=4.4,>=4.0 # Apache-2.0
+
+yamllint>=1.23.0