hyperv: avoid query memleaks on failure
    
    The function hypervEnumAndPull consumes query on success, but leaked
    it on failure.  Rather than having to change all callers (many of
    them indirect callers through the generated
    hypervGetMsvmComputerSystemList), it was easier to just guarantee
    that the buffer is cleaned on return from the function.
    
    * src/hyperv/hyperv_wmi.c (hypervEnumAndPull): Don't leak query on
    failure.
    
    Signed-off-by: Eric Blake <eblake@redhat.com>