Add the limitation of the nested container id length

[xiaowei]

Hi,

I am working on the issue MESOS-7168, to limit the nested container id 
length.
Considering the AUFS case [1] (thanks, Andy for pointing it out), we 
should set
the nested containerID limit to 242.
Please let me know if you have any concern.

[1] 
http://aufs.sourceforge.net/aufs3/man.html#Incompatible%20with%20an%20Ordinary%20Filesystem

Thanks,
Xiao Wei