Support filtering revision (documents) by any legal filter

This PS adds support for filtering revisions and
revision documents documents by any legal filter
(those enumerated in the design document).

Deckhand now supports the following filter arguments:
  * schema
  * metadata.name
  * metadata.label
  * metadata.layeringDefinition.abstract
  * metadata.layeringDefinition.layer
  * status.bucket

Deckhand now supports the following filter arguments for filtering
revisions:
  * tag

Deckhand now supports multiple filters, e.g.:
  * ?metdata.layeringDefinition.layer=site&metadata.name=foo

Deckhand now supports repeated filters, e.g.:
  * ?metadata.label=foo=bar&metadata.label=baz=qux

The following has yet to be implemented will be done in a future
follow-up PS:
  - support sorting by specific keywords as well
  - support query limit and offset filters

Change-Id: I8558481e075715fe7fab98140094d37782a986d9

deckhand/tests/functional/gabbits/revision-documents-multiple-filters.yaml

@@ -0,0 +1,65 @@
+# 1. Test success paths for filtering revision documents using multiple filters
+#    for the following filters:
+#   * metadata.label
+#   * metadata.layeringDefinition.abstract
+#   * metadata.layeringDefinition.layer
+# 2. Test success paths for multiple different-keyed filters.
+# 3. Test success paths for multiple same-keyed filters.
+
+defaults:
+  request_headers:
+    content-type: application/x-yaml
+  response_headers:
+    content-type: application/x-yaml
+
+tests:
+  - name: purge
+    desc: Begin testing from known state.
+    DELETE: /api/v1.0/revisions
+    status: 204
+
+  - name: initialize
+    desc: Create initial documents
+    PUT: /api/v1.0/bucket/mop/documents
+    status: 200
+    data: <@resources/design-doc-layering-sample.yaml
+
+  - name: filter_by_multiple_different_filters_expect_site
+    desc: Verify revision documents filtered by multiple repeated keys that are different
+    GET: /api/v1.0/revisions/$RESPONSE['$.[0].status.revision']/documents?metadata.layeringDefinition.layer=site&metadata.layeringDefinition.abstract=false
+    status: 200
+    response_multidoc_jsonpaths:
+      $.[0].metadata.name: site-1234
+      $.[0].metadata.layeringDefinition.layer: site
+      $.[0].metadata.layeringDefinition.abstract: false
+
+  - name: filter_by_multiple_different_filters_expect_region
+    desc: Verify revision documents filtered by multiple repeated keys that are different
+    GET: /api/v1.0/revisions/$RESPONSE['$.[0].status.revision']/documents?metadata.layeringDefinition.layer=region&metadata.layeringDefinition.abstract=true
+    status: 200
+    response_multidoc_jsonpaths:
+      $.[0].metadata.name: region-1234
+      $.[0].metadata.layeringDefinition.layer: region
+      $.[0].metadata.layeringDefinition.abstract: true
+
+  - name: filter_by_repeated_metadata_layeringDefinition_layer
+    desc: Verify revision documents filtered by multiple repeated keys that are the same
+    GET: /api/v1.0/revisions/$RESPONSE['$.[0].status.revision']/documents?metadata.layeringDefinition.layer=site&metadata.layeringDefinition.layer=region
+    status: 200
+    response_multidoc_jsonpaths:
+      $.[*].metadata.name:
+        - region-1234
+        - site-1234
+      $.[*].metadata.layeringDefinition.layer:
+        - region
+        - site
+
+  - name: filter_by_repeated_metadata_label
+    desc: Verify revision documents filtered by multiple repeated keys that are the same
+    GET: /api/v1.0/revisions/$RESPONSE['$.[0].status.revision']/documents?metadata.label=foo=bar&metadata.label=baz=qux
+    status: 200
+    response_multidoc_jsonpaths:
+      $.[0].metadata.name: site-1234
+      $.[0].metadata.labels:
+        foo: bar
+        baz: qux