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 of dom0 tools on domU functions.

Fixes bug: 1379804

Change-Id: I229e2d5f07070a9236ec612d4032c94c4361a9f6
Merge "XenAPI: workaround for unsupp. associative arrays"