Fix horizon config under Apache 2.4

Apache 2.4 now uses mod_authz_host for acces control. Horizon's
Apache config needs an update to allow access to its directory,
otherwise a 403 will be returned.
This change replaces a similar previous fixes done for Fedora 18
and Ubuntu 13.10, since this is an Apache version issue, not a
distro-specific one.

Change-Id: Iecc17600d8e1aae6a7b0929b1493d712c307616f
Closes-Bug: #1243075
diff --git a/functions b/functions
index 0a73b9f..5ca5eee 100644
--- a/functions
+++ b/functions
@@ -557,6 +557,18 @@
     [ "($uname -m)" = "$ARCH_TYPE" ]
 }
 
+# Checks if installed Apache is <= given version
+# $1 = x.y.z (version string of Apache)
+function check_apache_version {
+    local cmd="apachectl"
+    if ! [[ -x $(which apachectl 2>/dev/null) ]]; then
+        cmd="/usr/sbin/apachectl"
+    fi
+
+    local version=$($cmd -v | grep version | grep -Po 'Apache/\K[^ ]*')
+    expr "$version" '>=' $1 > /dev/null
+}
+
 # git clone only if directory doesn't exist already.  Since ``DEST`` might not
 # be owned by the installation user, we create the directory and change the
 # ownership to the proper user.
diff --git a/lib/horizon b/lib/horizon
index c116ec2..4cb2828 100644
--- a/lib/horizon
+++ b/lib/horizon
@@ -112,7 +112,12 @@
     # Create an empty directory that apache uses as docroot
     sudo mkdir -p $HORIZON_DIR/.blackhole
 
+    # Apache 2.4 uses mod_authz_host for access control now (instead of "Allow")
     HORIZON_REQUIRE=''
+    if check_apache_version "2.4" ; then
+        HORIZON_REQUIRE='Require all granted'
+    fi
+
     local horizon_conf=/etc/$APACHE_NAME/$APACHE_CONF_DIR/horizon.conf
     if is_ubuntu; then
         # Clean up the old config name
@@ -120,17 +125,7 @@
         # Be a good citizen and use the distro tools here
         sudo touch $horizon_conf
         sudo a2ensite horizon.conf
-        if [[ "$DISTRO" == "saucy" ]]; then
-            # Ubuntu 13.10 has Require all denied in apache2.conf
-            # and requires explicit Require all granted
-            HORIZON_REQUIRE='Require all granted'
-        fi
     elif is_fedora; then
-        if [[ "$os_RELEASE" -ge "18" ]]; then
-            # fedora 18 has Require all denied  in its httpd.conf
-            # and requires explicit Require all granted
-            HORIZON_REQUIRE='Require all granted'
-        fi
         sudo sed '/^Listen/s/^.*$/Listen 0.0.0.0:80/' -i /etc/httpd/conf/httpd.conf
     elif is_suse; then
         : # nothing to do