Fix pip install in mac

test=develop

Author: velconia

paddle/scripts/paddle_build.sh

@@ -384,7 +384,7 @@ EOF
         ctest --output-on-failure -j $1     
         # make install should also be test when unittest 
         make install -j 8
-        pip install /usr/local/opt/paddle/share/wheels/*.whl
+        pip install ${INSTALL_PREFIX:-/paddle/build}/opt/paddle/share/wheels/*.whl
         if [[ ${WITH_FLUID_ONLY:-OFF} == "OFF" ]] ; then
             paddle version
         fi