BUG/MEDIUM: proxy: must not try to stop disabled proxies upon reload

BUG/MEDIUM: proxy: must not try to stop disabled proxies upon reload

Hervé Commowick reported an issue : haproxy dies in a segfault during a
soft restart if it tries to pause a disabled proxy. This is because disabled
proxies have no management task so we must not wake the task up. This could
easily remain unnoticed since the old process was expected to go away, so
having it go away faster was not really troubling. However, with sync peers,
it is obvious that there is no peer sync during this reload.

This issue has been introduced in 1.5-dev7 with the removal of the
maintain_proxies() function. No backport is needed.