TST+BF: Use separate coveragerc for Travis CI

Should now ignore server/filtergamin.py as gamin is not tested. Also
ignores Travis CI python virtual environments.

Appears my syntax was wrong earlier, as "omit"s must be `,` or new line delimited.

Unfortunately their is no way to test these locally, without pushing commits and hoping you've not made a mistake :frowning:

Looks like all is working now however. Please see: https://coveralls.io/builds/11507