Reduce ngcp version string to something useable

Addressing:

| 15:26:25 + ec2-create-image --region eu-west-1 --name ngcp-ce-mr3.3.1.0+0~20140528091259.443+wheezy~1.gbpf74599 --description 'Official sip:provider CE AMI for release mr3.3.1.0+0~20140528091259.443+wheezy~1.gbpf74599 [2014-05-28_13:10]' i-b6b474f6
| 15:26:27 Client.InvalidAMIName.Malformed: AMI names must be between 3 and 128 characters long, and may contain letters, numbers, '(', ')', '.', '-', '/' and '_'