xenconfig: change 'hap' setting to align with Xen behavior

hap is enabled by default in xm and xl config and usually only
specified when it is desirable to disable hap (hap = 0). Change
the xm,xl <-> xml converter to behave similarly. I.e. only
produce 'hap = 0' when <hap state='off'/> and vice versa.

Signed-off-by: Jim Fehlig <jfehlig@suse.com>

tests/xlconfigdata/test-disk-positional-parms-partial.cfg

@@ -6,7 +6,6 @@ vcpus = 1
 pae = 1
 acpi = 1
 apic = 1
-hap = 0
 viridian = 0
 rtc_timeoffset = 0
 localtime = 0