CA-146595: Improve parsing of VM platform flags

We need to be able to use 0 and 1 in (at least) the case of the acpi key.
Before this patch, using 0 and 1 would have both been converted to true when
passed to Xenopsd and therefore wrong arguments could be passed to Qemu when
trying to disable this feature.

This patch makes the 'bool' function a little more lenient on its input rather
than using OCaml's stock bool_of_string. It also introduces a warning message
if the value has been specified incorrectly.

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>
Merge pull request #1947 from simonjbeaumont/ca-146595

CA-146595: Improve parsing of VM platform flags
CA-146736: Fix event registration after pool_migrate_complete

After running pool_migrate_complete, make sure the xapi events thread
re-registers so as to watch events for the newly-arrived VM.

Signed-off-by: John Else <john.else@citrix.com>
Merge pull request #1953 from johnelse/ca-146736

CA-146736: Fix event registration after pool_migrate_complete