provide proper default for $r10k_basedir

The variable basically contains the value from the
puppet_environmentpath fact. The default is
/etc/puppetlabs/code/environments. We can safely fallback to the
default value if the fact is undef. This allows the module to work
properly during the first run.

manifests/params.pp

@@ -10,7 +10,11 @@
   $sources                = undef
   $puppet_master          = true
 
-  $r10k_basedir              = $facts['puppet_environmentpath']
+  if $facts['puppet_environmentpath'] {
+    $r10k_basedir            = $facts['puppet_environmentpath']
+  } else {
+    $r10k_basedir            = '/etc/puppetlabs/code/environments'
+  }
   $r10k_cache_dir            = "${facts['puppet_vardir']}/r10k"
   $r10k_config_file          = '/etc/puppetlabs/r10k/r10k.yaml'
   $r10k_binary               = 'r10k'