Remove useless join in nova.virt.vmwareapi.vm_util

This change replaces in nova.virt.vmwareapi.vm_util the pattern
''.join(['fo...o'], ['b...ar']) by the pattern 'fo...ob...ar' which
avoids runtime string concatenation.

Change-Id: If23d8377acde2c3419b67ca11b03a1c898561c77
Merge "Remove useless join in nova.virt.vmwareapi.vm_util"