Even if this file is completely ignored because the role using it
is skipped, ansible parses the whole file. Any undefined variables
will cause a failure. Undefined variable was previously a way to
force failure if it was undefined, but now we have to do differently.
In the meantime, this is a quick fix to make sure we don't have
issues with undefined variables for non-multinode haproxy installs.
Change-Id: Ifd00f4eb0a0a3559d7d3bd3c5a4331798a3c96aa
Closes-Bug: 1631920