Only install packages if required on OSX

setup.sh

@@ -9,6 +9,9 @@ downloadHighPolySuv=true
 MIN_CMAKE_VERSION=3.10.0
 function version_less_than_equal_to() { test "$(printf '%s\n' "$@" | sort -V | head -n 1)" = "$1"; }
 
+# brew gives error if package is already installed
+function brew_install() { brew list $1 &>/dev/null || brew install $1; }
+
 # Parse command line arguments
 while [[ $# -gt 0 ]]
 do
@@ -63,7 +66,8 @@ if [ "$(uname)" == "Darwin" ]; then # osx
         sudo dseditgroup -o edit -a `whoami` -t user dialout
     fi
 
-    brew install wget coreutils
+    brew_install wget
+    brew_install coreutils
 
     if version_less_than_equal_to $cmake_ver $MIN_CMAKE_VERSION; then
         brew install cmake  # should get cmake 3.8