govet: allow analyzers suite configuration

[ernado]

Enabling or disabling go vet plug-ins would be very cool.
Seems like implementation is pretty straight-forward:

golangci-lint/pkg/golinters/govet.go

Lines 36 to 61 in c9a9255

	func NewGovet(cfg *config.GovetSettings) *goanalysis.Linter {
	analyzers := []*analysis.Analyzer{
	// the traditional vet suite:
	asmdecl.Analyzer,
	assign.Analyzer,
	atomic.Analyzer,
	bools.Analyzer,
	buildtag.Analyzer,
	cgocall.Analyzer,
	composite.Analyzer,
	copylock.Analyzer,
	errorsas.Analyzer,
	httpresponse.Analyzer,
	loopclosure.Analyzer,
	lostcancel.Analyzer,
	nilfunc.Analyzer,
	printf.Analyzer,
	shift.Analyzer,
	stdmethods.Analyzer,
	structtag.Analyzer,
	tests.Analyzer,
	unmarshal.Analyzer,
	unreachable.Analyzer,
	unsafeptr.Analyzer,
	unusedresult.Analyzer,
	}

We can filter analyzers in NewGovet function, but I'm not sure about config.
I think that there should be something like we have for linters section:

linters:
  enable:
    - megacheck
    - govet
  enable-all: false
  disable:
    - maligned
    - prealloc
  disable-all: false

But in linters-settings.govet.

Rel: #446