jira/client: Change JIRA base URL config handling

Right now the URL path of 'api/2/' is hard-coded in modules/jira/client. This
patch makes the whole path configurable. That means that the full path must be
specified in the config file and the library itself is not appending 'api/2/'
any more.

Change-Id: ac5c4243f3
Add support for CircleCI

Change-Id: a0cf9c84ca
Story-Id: SF-29