XenAPI: workaround for unsupp. associative arrays

Dom0's bash does not support associative arrays, however we source
`functions` and therefore our scripts fail. As a workaround, ignore
non-zero exit codes for the time of the sourcing. This way the execution
won't stop but we still get the relevant variable definitions from
localrc.

Fixes bug: 1379804

Change-Id: I229e2d5f07070a9236ec612d4032c94c4361a9f6
Get rid of sourcing completely

Change-Id: I7438c36bba375457db056a6415a2ce77afffb121