libbrillo: Add curl_multi_perform, curl_multi_wait wrappers. am: ed104e9 am: 9cadf91 am: 164017a
am: 6c4d550

* commit '6c4d5508fc1af4b1c8b9799aa455ae21fa4c9fd0':
  libbrillo: Add curl_multi_perform, curl_multi_wait wrappers.

Change-Id: Ideaaa1f45cca1eff67a02f1cebdba8096a2d9db6