rgw: rgw_admin also inits curl

rgw: rgw_admin also inits curl

since we use http manager which in turn uses curl and uses curl multi
interfaces. While curl is initialized at the first call of curl_easy_init() this
method isn't guaranteed to be safe when multiple threads may call the function
since curl_global_init isn't reentrant. Calling curl_global_init via
rgw::curl::setup_curl which additionally sets up ssl interfaces etc. when
openssl is used as curl's ssl backend. Similarly moving rgw target link to
accomodate this change.

Signed-off-by: Abhishek Lekshmanan <abhishek@suse.com>
(cherry picked from commit 112ba0b4dae5972b520aec39fe99275a6dfa899d)

 Conflicts:
  src/rgw/CMakeLists.txt
  beast submodule related changes which are not a part of this patchset
  src/rgw/rgw_admin.cc
  trivial whitespace conflicts #