Changes

asterisk: dnsmasq.conf: Avoid forwarding queries to other DNS servers

This creates problems when requesting resolution of the IPv6 address.
For some reason, dnsmasq was forwarding the request to the non-available
google DNS servers, and Asterisk docker container pre-start commands
checking for DNS resolution would never pass when run in jenkins node.

Change-Id: I0ee7a7b0c307cc83acfb1c4c8f4bdc092133fddb

asterisk: timeout ping DNS validations after 3 seconds

Change-Id: I9f1bcbc2b868cf7c894a57ca77e28b5bfbba0eac

asterisk: Wait for Asterisk ready before starting testsuite

A recent commit made Asterisk wait for dnsmasq to be ready before
starting it. This means Asterisk takes more time now to be ready itself,
hence we need to delay launching the testsuite until it is ready.
Otherwise, the entire set of tests may be run even before Asterisk gets
to answer on the AMI socket.

Change-Id: I337d57f3eb3e6688dbf3c61d55978da10d84b2cb