Return True after yummain runs.

Capture the errcode returned, but don't do anything for now.  It's
probably likely that yummain will always fail according to it
because our instroot won't have everything in place that scriplets
need to run.  But scriptlets are supposed to always exit with
success, so I dunno.

src/pylorax/instroot.py

@@ -122,4 +122,7 @@ def installPackages(yumconf=None, destdir=None, packages=None):
     arglist.append("--installroot=%s" % (destdir,))
     arglist += ['install', '-y'] + packages
 
-    return yummain.user_main(arglist, exit_code=False)
+    # XXX: sort through yum errcodes and return False for actual bad things
+    # we care about
+    errcode = yummain.user_main(arglist, exit_code=False)
+    return True