Add Travis testing

Thanks @geerlingguy!
Do not do sysctl stuff on travis runs

Adds the redis_travis_ci variable, which won't run the sysctl stuff
when the role is run via Travis CI. They appear to be blocking these
changes.
Add status reporting for Debian init script

For #14, but also a requirement for Travis idempotency check in #19
Add Redis smoke test
Add Travis build icon thingy
Merge pull request #19 from DavidWittman/travis

Add Travis testing
Remove test inventory file

ansible and ansible-playbook allow you to pass in hosts without an
inventory file by appending a comma to the host list. I find this a
little cleaner than having a localhost inventory file.
Don't gather facts on single install test run
We do need to gather facts after all
Merge pull request #20 from DavidWittman/test-remove-inventory-file

Remove test inventory file
Use LSB functions in sentinel init script

Also fixes bind address config issue from #7
Add BIND_ADDRESS to init config file for Debian

Also only includes the REDIS_PASSWORD when it's set.
Update Travis tests for Sentinel
Bugfixes for Sentinel testing

 - Define monitor list in test_sentinel.yml playbook
 - Set Sentinel bind address in init config file appropriately
 - Don't insert Sentinel config options if they're False
Merge pull request #21 from DavidWittman/sentinel-tests

Sentinel tests
Document the Redis install path in the README

Per #11