rgw: fix more warnings

test/test_rgw_admin_opstate.cc: In member function 'int admin_log::test_helper::extract_input(int, char**)':
warning: test/test_rgw_admin_opstate.cc:129:24: comparison between signed and unsigned integer expressions [-Wsign-compare]
warning: test/test_rgw_admin_opstate.cc:131:24: comparison between signed and unsigned integer expressions [-Wsign-compare]
warning: test/test_rgw_admin_opstate.cc:133:24: comparison between signed and unsigned integer expressions [-Wsign-compare]
warning: test/test_rgw_admin_opstate.cc:135:24: comparison between signed and unsigned integer expressions [-Wsign-compare]

test/test_rgw_admin_log.cc: In member function 'int admin_log::test_helper::extract_input(int, char**)':
warning: test/test_rgw_admin_log.cc:132:24: comparison between signed and unsigned integer expressions [-Wsign-compare]
warning: test/test_rgw_admin_log.cc:134:24: comparison between signed and unsigned integer expressions [-Wsign-compare]
warning: test/test_rgw_admin_log.cc:136:24: comparison between signed and unsigned integer expressions [-Wsign-compare]
warning: test/test_rgw_admin_log.cc:138:24: comparison between signed and unsigned integer expressions [-Wsign-compare]

Signed-off-by: Sage Weil <sage@inktank.com>