Fix error message for extra files on non MC nodes
Fix error message for extra files on non MC nodes

Currently the message for extraneous files on non master candidates is
confusing, to say the least. This makes it hopefully more clear.

Signed-off-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>
Reviewed-by: Olivier Tharan <0947fcc917eb1d3c89ad818beb61e3b2c3cf3bba@google.com>

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