Return correct failure data from Node.add*
Return correct failure data from Node.add*

This patch alters the Node.addPri/addSec to return correct failure data.
It removes the computeFailN1 function from the module as that used to
combine both mem and disk checks in the same function and thus the real
error reason cannot be deduced when using it.

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