lxd init: accept empty trust password
lxd init: accept empty trust password

Signed-off-by: Serge Hallyn <3df611b026e4639bee8aef7a4beb2e39fcebb313@ubuntu.com>

lxc/lxd,mjeanson/lxd,ollie314/lxd,stgraber/lxd,hallyn/lxd,lxc/lxd,lxc/lxd,atxwebs/lxd,hallyn/lxd,stgraber/lxd,stgraber/lxd,stgraber/lxd,akshaykarle/lxd,stgraber/lxd,akshaykarle/lxd,erikmack/lxd,lxc/lxd,hallyn/lxd,georghopp/lxd,pcdummy/lxd,chrisglass/lxd,chrisglass/lxd,jsavikko/lxd,erikmack/lxd,georghopp/lxd,techtonik/lxd,Skarlso/lxd,Skarlso/lxd,atxwebs/lxd,jsavikko/lxd,hallyn/lxd,ollie314/lxd,techtonik/lxd,yura-pakhuchiy/lxd,yura-pakhuchiy/lxd,hallyn/lxd,pcdummy/lxd,lxc/lxd,lxc/lxd,erikmack/lxd,mjeanson/lxd,akshaykarle/lxd,atxwebs/lxd,Skarlso/lxd,pcdummy/lxd,jsavikko/lxd,techtonik/lxd,stgraber/lxd,georghopp/lxd,Skarlso/lxd,hallyn/lxd,atxwebs/lxd,stgraber/lxd,ollie314/lxd,lxc/lxd,yura-pakhuchiy/lxd,mjeanson/lxd,chrisglass/lxd