qemu_namespace: Rename variable

qemu_namespace: Rename variable

The boolean actually tells whether the file existed when the function
was called and using it in more places later on makes them
confusing (e.g. do something with a file if it does not exist).  To
better reflect the above and prepare for next patch rename this
variable.

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>