Update to use go modules (#671)

This includes updates to CI config, vendor files, etc.
I've hard-coded the k8s depedency at 1.13.4 to keep it inline with what
we currently have and to make sure a another run of `go mod tidy`
doesn't accidentally update it to an unexpected version.

Thanks to hectorj2f for carrying this along.

vendor/github.com/hashicorp/golang-lru/.gitignore

@@ -0,0 +1,23 @@
+# Compiled Object files, Static and Dynamic libs (Shared Objects)
+*.o
+*.a
+*.so
+
+# Folders
+_obj
+_test
+
+# Architecture specific extensions/prefixes
+*.[568vq]
+[568vq].out
+
+*.cgo1.go
+*.cgo2.c
+_cgo_defun.c
+_cgo_gotypes.go
+_cgo_export.*
+
+_testmain.go
+
+*.exe
+*.test

vendor/github.com/hashicorp/golang-lru/README.md

@@ -0,0 +1,25 @@
+golang-lru
+==========
+
+This provides the `lru` package which implements a fixed-size
+thread safe LRU cache. It is based on the cache in Groupcache.
+
+Documentation
+=============
+
+Full docs are available on [Godoc](http://godoc.org/github.com/hashicorp/golang-lru)
+
+Example
+=======
+
+Using the LRU is very simple:
+
+```go
+l, _ := New(128)
+for i := 0; i < 256; i++ {
+    l.Add(i, nil)
+}
+if l.Len() != 128 {
+    panic(fmt.Sprintf("bad len: %v", l.Len()))
+}
+```

vendor/github.com/hashicorp/golang-lru/go.mod

@@ -0,0 +1 @@
+module github.com/hashicorp/golang-lru

vendor/github.com/hashicorp/golang-lru/lru.go

@@ -40,31 +40,35 @@ func (c *Cache) Purge() {
 // Add adds a value to the cache.  Returns true if an eviction occurred.
 func (c *Cache) Add(key, value interface{}) (evicted bool) {
 	c.lock.Lock()
-	defer c.lock.Unlock()
-	return c.lru.Add(key, value)
+	evicted = c.lru.Add(key, value)
+	c.lock.Unlock()
+	return evicted
 }
 
 // Get looks up a key's value from the cache.
 func (c *Cache) Get(key interface{}) (value interface{}, ok bool) {
 	c.lock.Lock()
-	defer c.lock.Unlock()
-	return c.lru.Get(key)
+	value, ok = c.lru.Get(key)
+	c.lock.Unlock()
+	return value, ok
 }
 
 // Contains checks if a key is in the cache, without updating the
 // recent-ness or deleting it for being stale.
 func (c *Cache) Contains(key interface{}) bool {
 	c.lock.RLock()
-	defer c.lock.RUnlock()
-	return c.lru.Contains(key)
+	containKey := c.lru.Contains(key)
+	c.lock.RUnlock()
+	return containKey
 }
 
 // Peek returns the key value (or undefined if not found) without updating
 // the "recently used"-ness of the key.
 func (c *Cache) Peek(key interface{}) (value interface{}, ok bool) {
 	c.lock.RLock()
-	defer c.lock.RUnlock()
-	return c.lru.Peek(key)
+	value, ok = c.lru.Peek(key)
+	c.lock.RUnlock()
+	return value, ok
 }
 
 // ContainsOrAdd checks if a key is in the cache  without updating the
@@ -98,13 +102,15 @@ func (c *Cache) RemoveOldest() {
 // Keys returns a slice of the keys in the cache, from oldest to newest.
 func (c *Cache) Keys() []interface{} {
 	c.lock.RLock()
-	defer c.lock.RUnlock()
-	return c.lru.Keys()
+	keys := c.lru.Keys()
+	c.lock.RUnlock()
+	return keys
 }
 
 // Len returns the number of items in the cache.
 func (c *Cache) Len() int {
 	c.lock.RLock()
-	defer c.lock.RUnlock()
-	return c.lru.Len()
+	length := c.lru.Len()
+	c.lock.RUnlock()
+	return length
 }