Merge branch 'release/0.2.7' into develop
Prevent calls being dropped for lack of media

In newer versions of Asterisk (at least 11.6) when no audio is being played to a channel, no RTP is sent.  This can cause clients to hang up. For example, Blink terminates the call 30 seconds after receiving no audio.  Adding an RTP keepalive prevents this.
Update kitchen config
Test on CentOS
Ensure prereqs get installed across platforms
Use provided init script, which works across platforms
Update unimrcp cookbook for CentOS compat
Update test-kitchen to a stable release
Support package install on CentOS

Test with project repos
Claim support on CentOS
Bump to 0.3.0
Merge branch 'release/0.3.0'