add guard for auto-running tests

Gemfile

@@ -8,3 +8,7 @@ bosh_cli_path = File.expand_path("~/gems/cloudfoundry/bosh/bosh_cli")
 if File.directory?(bosh_cli_path)
   gem "bosh_cli", path: bosh_cli_path
 end
+
+group :development do
+  gem "guard-rspec"
+end

Guardfile

@@ -0,0 +1,7 @@
+guard 'rspec', spec_paths: ["spec"] do
+  watch(%r{^spec/(.+_spec)\.rb$})
+  watch(%r{^lib/bosh/cli/commands/(.+)\.rb$})    { |m| "spec/plugin_spec.rb" }
+  watch(%r{^lib/bosh/cloudfoundry/(.+)\.rb$})    { |m| "spec/#{m[1]}_spec.rb" }
+  watch('spec/spec_helper.rb')  { "spec" }
+end
+