Changes

asterisk: Use Titan TEXT encoder to implement AMI record enc/dec

f_ami_wait_for_prompt_str had to be fixed since it was returning content
like this:
"Response: Success\nMessage: Authentication accepted"
Instead, the TEXT encoding expects:
"Response: Success\nMessage: Authentication accepted\n"
which is actually more in line with proper expectancies.

Change-Id: If179e45307a7e42b81b28db6ee4b7bf5eeb8b5f1