Expand template path under user's home directory.

* File.join won't expand `~` into `ENV['HOME']`
  (http://ruby-doc.org/core-1.9.3/File.html#method-c-expand_path)
* The FakeFS File.exists? implementation calls FileSystem#find
  (https://github.com/defunkt/fakefs/blob/master/lib/fakefs/file_system.rb#L22-33)
  containing a call to FileSystem#normalize_path which expands the
  path variable passed in
  (https://github.com/defunkt/fakefs/blob/master/lib/fakefs/file_system.rb#L91-98)
* The file system mocking library sets up a false expectation that `~`
  will be expanded in the #export_template method and consequently the
  production code can't use the template directory
* To guard against future regressions such as fixes/updates to FakeFS or
  using an alternate file system mocking library, the specs were updated
  to explicitly set `ENV['HOME']`

lib/foreman/export/base.rb

@@ -26,7 +26,7 @@ private ######################################################################
   def export_template(exporter, file, template_root)
     if template_root && File.exist?(file_path = File.join(template_root, file))
       File.read(file_path)
-    elsif File.exist?(file_path = File.join("~/.foreman/templates", file))
+    elsif File.exist?(file_path = File.expand_path(File.join("~/.foreman/templates", file)))
       File.read(file_path)
     else
       File.read(File.expand_path("../../../../data/export/#{exporter}/#{file}", __FILE__))