Install: Fix use of DEBIAN_FRONTEND - `sudo` clears environment

Before executing a command, for security reasons `sudo` clears the
environment, so the value of DEBIAN_FRONTEND was never passed to
apt-get. This was causing the mysql packqge to still prompt for
a value interactively.

scripts/install-system-req.sh

@@ -35,18 +35,13 @@ case `uname -s` in
             squeeze|wheezy|jessie|maya|lisa|olivia|nadia|natty|oneiric|precise|quantal|raring)
                 output "Installing Debian family requirements"
 
-                # DEBIAN_FRONTEND=noninteractive is required for silent mysql-server installation
-                export DEBIAN_FRONTEND=noninteractive
-
                 # add repositories
                 cat $APT_REPOS_FILE | xargs -n 1 sudo add-apt-repository -y
-                sudo apt-get -y update
-                sudo apt-get -y install gfortran
-                sudo apt-get -y install graphviz libgraphviz-dev graphviz-dev
-                sudo apt-get -y install libatlas-dev libblas-dev 
-                sudo apt-get -y install ruby-rvm
+                sudo apt-get -yq update
+                sudo DEBIAN_FRONTEND=noninteractive apt-get -yq install gfortran graphviz \
+                            libgraphviz-dev graphviz-dev libatlas-dev libblas-dev ruby-rvm
                 # install packages listed in APT_PKGS_FILE
-                cat $APT_PKGS_FILE | xargs sudo apt-get -y install
+                cat $APT_PKGS_FILE | xargs sudo DEBIAN_FRONTEND=noninteractive apt-get -yq install
                 ;;
             *)
                 error "Unsupported distribution - $distro"