Improve pylintrc for pylint 0.21+
Improve pylintrc for pylint 0.21+

While we'll need to update the source files too, at least this change
makes pylint 0.21 not fail on the current source tree.

Signed-off-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>
Reviewed-by: Guido Trotter <f62ca4d5358bdaeef0e50e57f9f7e231de63727e@google.com>

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