The version fact currently supplies the available redis version

regardless of whether it's installed or not. The result is that
all nodes contain a fact that implies that the latest available
redis version seems to be installed.

This change switches from using yum to rpm to query the locally
installed package database. It has the added benefit of not
querying yum, which can be costly.

Addresses fsalum#39 in part.

lib/facter/redis_version.rb

@@ -40,14 +40,14 @@
 
     setcode do
 
-        yum = `which yum 2> /dev/null`.chomp
-        if yum == ''
-            yum = '/usr/bin/yum'
+        rpm = `which rpm 2> /dev/null`.chomp
+        if rpm == ''
+            rpm = '/usr/bin/rpm'
         end
 
         redis_version = Facter::Util::Resolution.exec('/usr/sbin/redis-server --version')
         if redis_version.nil?
-            redis_version = Facter::Util::Resolution.exec(yum+" info redis 2> /dev/null | /bin/grep '^Version' | /bin/awk -F ':' '{printf(\"%s\",$2)}' | sort -nr | head -1")
+            redis_version = Facter::Util::Resolution.exec(rpm+" -q --queryformat '%{version}\\n' redis | grep -v 'not installed' | sort -nr | head -1")
         end
 
         case redis_version
@@ -64,7 +64,7 @@
                 #set version to 2.2
                 redis_version = '2.2.x'
             else
-                redis_version = 'nil'
+                redis_version = nil
         end
         redis_version
   end