It looks like vstart.sh does not work without authx enabled. Given that, 
I'd propose to change the default to having cephx be enabled and then 
use the -x flag to disable cephx.

Interestingly enough, the help output for vstart.sh already states that 
the -x flag disables authx (which is not the case at present, but is 
after this patch is applied).

I've attached a patch to vstart that 1) changes the mention of authx to 
cephx for consistency and 2) defaults vstart.sh to using cephx with the 
-x flag now serving to disable cephx.

Best,
-Joe Buck