This patch fixes the broken devstack plugin script and slightly changes
the way the var IS_ZUUL_FT is used. When the var is unset, a bash unary
operator expected error should've been emitted because of this part:
${IS_ZUUL_FT+yes}. Unset vs set was a bit confusing so this patch not
only fixes the part but forces the var into always being set and changes
it to "True" vs "False".
Change-Id: I25b418f7776d0d9a00fcf7846a406aba62d40190
d5eac3c31a