feat(BaseService): add new method configure_service to BaseService class & enhance vcap parsing

[jorge-ibm]

Fixes: https://github.ibm.com/arf/planning-sdk-squad/issues/1142

Changes:

• moved the external configuration code outside of the constructor into it's own method.
• for compatibility, the constructor calls the new method until we move to the service factory's complete implementation.
• disable_ssl is now also configurable from external config to be consistent with the other cores.
• (Potential bug fix) moved the instantiation of @conn in the constructor, to prior to configuring the http client. Before, if disable ssl was set to true through the constructor arguments, this would cause a failure in the configure_http_client method.
• enhanced vcap parsing to follow the latest service factory design
• Added a unit test for utility methods
• Added CONTRIBUTING.md since apparently this was missing 😄

[jorge-ibm]

Hi - @padamstx, @mkistler, @mamoonraja these changes are ready for review.

[jorge-ibm]

Hi @padamstx - this is ready for re-review.

[padamstx]

@mamoonraja could you please give this PR a look. Our main goals in this PR are: 1) Enhance the VCAP config loading algorithm to comply with our service config feature design, specially this section. 2) Fix some minor quirks related to loading service-level properties from external config sources.

There will be some minor changes to the Ruby generator that will go along with this Ruby core update. The plan would be to merge both PRs into the respective master branches at about the same time (@jorge-ibm is working on the Ruby generator updates now).

[watson-github-bot]

:tada: This PR is included in version 1.1.0 :tada:

The release is available on GitHub release

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