install sudo since the default 16.04 image doesn't seem to contain it

Summary:
Some of our tests require sudo and the docker image doesn't have it by
default: https://travis-ci.org/facebook/openr/builds/306157670.

Reviewed By: saifhhasan

Differential Revision: D6406044

fbshipit-source-id: 6ec07fcc6b4eabce408d50f5656f9e391e4bd883

build/fbcode_builder/fbcode_builder.py

@@ -206,6 +206,7 @@ class FBCodeBuilder(object):
                 'libtool '
                 'netcat-openbsd '
                 'pkg-config '
+                'sudo '
                 'unzip '
                 'wget'
             )),