BUG/MINOR: http-rules: Fix memory releases on error path during action parsing

BUG/MINOR: http-rules: Fix memory releases on error path during action parsing

When an error occurred during the parsing of an HTTP action, if some memory was
allocated, it should be released before exiting. Sometime a call to free() is
used on a sample expression instead of a call to release_sample_expr(). Other
time, it is just a string or a regex that should be released.

There is no real reason to backport this patch. Especially because this part was
highly modified recentely in 2.2-DEV.