improve code checking

Use goimports to check code:
goimports checks what gofmt does plus it keeps imports in specific
order. In this patch we:
- replace gofmt with goimports
- add code format checking to travis
- reorganize Makefile a little bit
- remove make generate-manifests from README.md since it is not needed
  during the development process
- add Makefile target for operator-sdk build k8s

Add whitespace check and auto-formatting:
I hate trailing whitespaces. This patch adds automated check detecting
any and Makefile target removing them.

Add codegen validation:
Add a check validating that generated code is up to date. This would
fail on travis in case a contributor forget to run `make generate-api`.

ship and goimports operator-sdk in vendor/:
In order to make sure everyone uses the same version of operator-sdk
producing the same code, let's keep operator-sdk in vendoring. The
same for goimports.

Signed-off-by: Petr Horacek <phoracek@redhat.com>

.gitignore

@@ -12,3 +12,12 @@ cluster/.kubectl
 
 # Cover file
 cover.out
+
+# Makefile fake targets
+gen-k8s
+gen-k8s-check
+goimports
+goimports-check
+vet
+whitespace
+whitespace-check

.travis.yml

@@ -1,12 +1,12 @@
 language: go
-go: "1.10"
+go: "1.11"
 
 services:
 - docker
 
 install: true
 script:
-- make test 
+- make check
 - make docker-build
 
 deploy:
@@ -16,7 +16,7 @@ deploy:
   on:
     branch: master
 - provider: script
-  script: docker login -u="$DOCKER_USER" -p="$DOCKER_PASS" quay.io && make docker-build docker-push IMAGE_TAG=$TRAVIS_TAG 
+  script: docker login -u="$DOCKER_USER" -p="$DOCKER_PASS" quay.io && make docker-build docker-push IMAGE_TAG=$TRAVIS_TAG
   skip_cleanup: true
   on:
     tags: true