Task name crashes Mesos-DNS

[sargun]

If you start a marathon app named hello------------------------------------------------------------------------------------------------------------------------------f it crashes mesos-dns. This is due to the creativity involved in the labels.trimCut function.

@jdef I propose we simplify this function. I say we make it trims the left characters, and then it trims the right characters, and if it is still too long, it just truncates it.

[drewkerrigan]

@sargun can this be closed?