TestCommon: Add listOfUniqueBy
TestCommon: Add listOfUniqueBy

This is a Gen for creating elements that are distinct by a certain property,
(e.g. for generating a list of jobs, all of which have different job IDs).

Signed-off-by: Niklas Hambuechen <98215d3a72cb13cc9c9956528e50119ca7d1fb8b@google.com>
Reviewed-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>

yiannist/ganeti,ganeti/ganeti,apyrgio/ganeti,ganeti-github-testing/ganeti-test-1,onponomarev/ganeti,yiannist/ganeti,andir/ganeti,grnet/snf-ganeti,leshchevds/ganeti,dimara/ganeti,yiannist/ganeti,mbakke/ganeti,ganeti-github-testing/ganeti-test-1,leshchevds/ganeti,bitemyapp/ganeti,apyrgio/ganeti,mbakke/ganeti,onponomarev/ganeti,mbakke/ganeti,grnet/snf-ganeti,bitemyapp/ganeti,andir/ganeti,dimara/ganeti,ganeti/ganeti,ganeti/ganeti,andir/ganeti,leshchevds/ganeti