Add kubectl package

packages/kubectl.rb

+require 'package'
+
+class Kubectl < Package
+  description 'Kubernetes command line tool'
+  homepage 'https://kubernetes.io'
+  version '1.7.0'
+  source_url 'https://github.com/kubernetes/kubernetes/archive/v1.7.0.tar.gz'
+  source_sha256 '0fe34180a4bb61384894616b1d348cc6350d1ebcbc071c67748864ffd2deb026'
+
+  depends_on "go" => :build
+  depends_on "rsync" => :build
+
+  def self.build
+    ENV['TMPDIR'] = "#{CREW_PREFIX}/tmp"
+    # Override the -j$NPROC set by crew with -j1 to workaround a race issue
+    system "make", "-j1", "generated_files"
+    system "make", "kubectl"
+  end
+
+  def self.install
+    system "install", "-D", "-m", "755", "_output/bin/kubectl", "#{CREW_DEST_DIR}/usr/local/bin/kubectl"
+  end
+end