Delete stored nonces on successful authentication to prevent replay attacks; also set a Chronos timer so that we send an AUTHENTICATION_TIMEOUT Server-Assignment-Request to the HSS if authentication hasn't completed within 30s
Code review feedback - proper handling of error cases
Conform to new ChronosConnection API where you configure a host/port up front. Also use  for the HTTP listen port
Take master cpp-common
Merge remote-tracking branch 'origin/dev' into authentication_timeout
Fix up UTs after last change
Merge pull request #464 from Metaswitch/authentication_timeout

[Reviewer: Ellie] Handle authentication timeouts