XenAPI: workaround for unsupp. associative arrays

Dom0's bash does not support associative arrays, however we source
`functions` and therefore our scripts fail. This change breaks the
dependency od dom0 tools on domU functions. Some dummy values had to be
put in place to avoid failure while installing neutron plugins.

Fixes bug: 1379804

Change-Id: I229e2d5f07070a9236ec612d4032c94c4361a9f6