build: add yaml file linting to make checkstyle

Type: feature

fts and trex rely on yaml config files.  Verify
that they are valid, so comitters can catch
errors early.

Change-Id: Ide0bb276659119c59bdbbc8b8155e37562a648b8
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>

src/plugins/flowprobe/FEATURE.yaml

@@ -1,3 +1,4 @@
+---
 name: IPFIX probe
 maintainer: Ole Troan <ot@cisco.com>
 features:
@@ -6,8 +7,8 @@ features:
   - Recording of L2, L3 and L4 information
 description: "IPFIX flow probe. Works in the L2, or IP input feature path."
 missing:
- - Output path
- - Export over IPv6
- - Export over TCP/SCTP
+  - Output path
+  - Export over IPv6
+  - Export over TCP/SCTP
 state: production
 properties: [API, CLI, STATS, MULTITHREAD]