Adjust role import to account for possible colon in role name

[bskinn]

The .. rst:directive:option:: directive was added in around the Sphinx v2.2 timeframe, which introduces a role with an internal colon: directive:option. Name import needs to account for this.

Might explain some of the deviation observed in some of the test .inv files.

Shouldn't need any new tests other than the suite of objects.inv checks.