v0.0.55: Licence agreement change fix

Fixes #191, whereby acmetool did not correctly respond to changes in an
ACME server's preferred agreement. This is an important update and should
be applied promptly, as it causes autorenewal to fail (though by design,
acmetool requires intervention to agree to new agreements anyway).

Implements new option as per #178, where HTTP self-testing
can be disabled.

Fixes #186, whereby there is a small chance of a DNS
token string being interpreted as an option to grep in
the example DNS hook included in the repository.

The dependency on degoutils has been removed in favour
of a marginally more stable version.

Fixes #175, whereby HAProxy symlinks are now forcibly replaced.

Fixes #171, whereby the haproxy directory could be created
world-readable in some circumstances.

Miscellaneous release engineering changes related to changes
in boulder.