bhyve: fix bhyveargv2xml custom loader test

Before pushing this test, I changed the appropriate args file
to pet test-wrap-argv.pl, but forgot to change the xml file, so
update it accordingly.

tests/bhyveargv2xmldata/bhyveargv2xml-custom-loader.xml

@@ -5,7 +5,7 @@
   <currentMemory unit='KiB'>219136</currentMemory>
   <vcpu placement='static'>1</vcpu>
   <bootloader>/usr/bin/custom-loader</bootloader>
-  <bootloader_args>with several arguments</bootloader_args>
+  <bootloader_args>-s ome --args</bootloader_args>
   <os>
     <type>hvm</type>
   </os>