import and install gettext in vm_vdi_cleaner.py

importing some nova modules expects _() to be defined, so lets define it
before we start importing them.

Change-Id: I7f951a24c19a53434c090cd2c01eded77c703943
Merge "import and install gettext in vm_vdi_cleaner.py"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp