Handle the result of QueryGroups() correctly
Handle the result of QueryGroups() correctly

If no group is given for the “gnt-network connect“/“… disconnect”
commands, the client uses the result of “QueryGroups()” which is a list
of lists. Use “itertools.chain()” to handle the return value correctly.

Signed-off-by: Dimitris Aragiorgis <4514117c4a99256e19437c7e3407c4ecbf98aec0@grnet.gr>
Signed-off-by: Michael Hanselmann <68b67885ff74281219b4a4be33cc20fd45078d7c@google.com>
Reviewed-by: Dimitris Aragiorgis <4514117c4a99256e19437c7e3407c4ecbf98aec0@grnet.gr>
Reviewed-by: Michael Hanselmann <68b67885ff74281219b4a4be33cc20fd45078d7c@google.com>
(cherry picked from commit af3aea481c3b8528239770edcae75d406a57de81)

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