make passing env vars work across guest OS suites

bin/gbuild

@@ -84,7 +84,7 @@ def build_one_configuration(suite, arch, build_desc, reference_datetime)
   system! "on-target -u root apt-get update > var/install.log 2>&1"
 
   info "Installing additional packages (log in var/install.log)"
-  system! "on-target -u root DEBIAN_FRONTEND=noninteractive apt-get --no-install-recommends -y install #{build_desc["packages"].join(" ")} > var/install.log 2>&1"
+  system! "on-target -u root -e DEBIAN_FRONTEND=noninteractive apt-get --no-install-recommends -y install #{build_desc["packages"].join(" ")} > var/install.log 2>&1"
 
   info "Grabbing package manifest"
   system! "on-target -u root bash < target-bin/grab-packages.sh > var/base-#{suitearch}.manifest"

libexec/on-target

@@ -10,7 +10,8 @@ usage() {
   echo
   cat << EOF
   --help		display this help and exit
-  --user <username>	run as <username> instead of ubuntu
+  --user|-u <username>	run as <username> instead of ubuntu
+  --env|-e "NAME=VALUE ..."	modify the environment
 EOF
 }
 
@@ -25,6 +26,10 @@ if [ $# != 0 ] ; then
         TUSER="$2"
         shift 2
         ;;
+      --env|-e)
+        ENV="$2"
+        shift 2
+        ;;
       --*)
         echo "unrecognized option $1"
         exit 1
@@ -45,9 +50,5 @@ if [ -z "$USE_LXC" ]; then
     ssh -oConnectTimeout=30 -oNoHostAuthenticationForLocalhost=yes -i ${GITIAN_BASE:-.}/var/id_dsa -p $VM_SSH_PORT $TUSER@localhost $*
 else
     config-lxc
-    if [ $TUSER = "root" ]; then
-        sudo lxc-start -n gitian -f var/lxc.config -- sh -c "sudo -i -- $*"
-    else
-        sudo lxc-start -n gitian -f var/lxc.config -- sh -c "sudo -i -u $TUSER -- $*"
-    fi
+    sudo lxc-start -n gitian -f var/lxc.config -- sudo -u $TUSER $ENV -i -- $*
 fi