Virt: fix typo (flavour should be flavor)

Commit 0c74df4962f256d9bc17b57c22ea45ece94e2f1a added support
which used the word flavour. Flavour is the preferred
spelling throughout the rest of the English-speaking world, but
flavor is preferrred spelling for OpenStack.

TrivialFix

Change-Id: I5fb3dd1601324c6be4f4d159166f5cacbec16a7e
Merge "Virt: fix typo (flavour should be flavor)"