Allow to use custom repository

[amarao]

We have a policy to use local mirrors for all external packages. That means, to use clickhouse in production I need to create a local mirror and to change the ansible-clickhouse role to use that mirror.

When I've tried to use custom clickhouse_repo variable I found that ansible-clickhouse uses 'include_vars' which overrides variables from the calling playbook. Moreover, I found that all three files to include (vars/Ubuntu_trusty.yml, Ubuntu_precise.yml and Ubuntu_xenial.yml) are identical (except for a single empty line).

To achieve my goal (use of custom repositories) I'd like to do four things:

1. Move all variables from Ubuntu* files into defaults.
2. Remove include_var statement
3. Add variable clickhouse_repo_key_data (not defined by default).
4. In case of clickhouse_repo_key_data make role to use it instead of clickhouse_repo_keyserver and clickhouse_repo_key to add that key into apt_key (with data option).

Is it ok?

[amarao]

Oh, it's more complicated then I expected. I'll leave 'include' section for 'clickhouse_supported' but will move repo/key things to defaults. Is it ok?

[krzyzakp]

I think it should be okay. I also don't know, why it was per Distro included.
When my PR #16 will be merged, we can see if it's working in TravisCI.

[krzyzakp]

@amarao Could you make PR for your commit, to get your changes done and also resolve this issue?

[amarao]

I done this in #17