Revert "Remove option for not raising exceptions for now."

This reverts commit 5e5ed91, putting
back the option to prevent exceptions from being raised.

lib/puppet/functions/vault_lookup/lookup.rb

@@ -2,9 +2,21 @@
   dispatch :lookup do
     param 'String', :path
     param 'String', :vault_url
+    optional_param 'Boolean', :raise_exceptions
   end
 
-  def lookup(path, vault_url)
+  def lookup(path, vault_url, raise_exceptions = true)
+    _lookup(path, vault_url)
+  rescue StandardError => e
+    raise if raise_exceptions
+
+    Puppet.err(e.message)
+    nil
+  end
+
+  private
+
+  def _lookup(path, vault_url)
     uri = URI(vault_url)
     # URI is used here to just parse the vault_url into a host string
     # and port; it's possible to generate a URI::Generic when a scheme
@@ -31,8 +43,6 @@ def lookup(path, vault_url)
     Puppet::Pops::Types::PSensitiveType::Sensitive.new(data)
   end
 
-  private
-
   def get_auth_token(connection)
     response = connection.post('/v1/auth/cert/login', '')
     unless response.is_a?(Net::HTTPOK)