CA-141364: Remove wasted hypercalls on domain build

The HPET and VPT are enabled or otherwise within Xenguest. Doing so here is
unnecessary.

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
CA-141364: Don't ignore errors from libxc on domain build

Failures from these calls are fatal and we should not continue with any VM
build (start, resume) operations if these calls return an error.

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Merge pull request #1878 from simonjbeaumont/ca-141364-xs64bit

[xs64bit] CA-141364: Handle errors during domain build