CA-109013: Revert "Making the check for both types of migrations"

This check doesn't work as is in the cross-pool case, since
the destination host won't be in the local database.

This reverts commit b79b9d0779a903911aa9e33796d3a127102848f4.
Support remote hosts in Helpers.version_string_of

Signed-off-by: John Else <john.else@citrix.com>
Add platform version check to cross-pool migration

Signed-off-by: John Else <john.else@citrix.com>
CA-89974: Live migrate fails on IPv6-preferring hosts

Make HTTP client embed IPv6 literal addresses correctly in URLs. A
related commit to xen-api-libs makes the HTTP server understand such URLs.

This commit removes 'Helpers.validate_ip_address' from
xapi/helpers.ml. The related commit to xen-api-libs adds it to
stdext/unixext.ml, renaming it to 'domain_of_addr'.

Signed-off-by: Euan Harris <euan.harris@citrix.com>
CA-97402: Add a means of disabling modules in the domainjoin-cli command.

Signed-off-by: John Else <john.else@citrix.com>
Merge pull request #1317 from euanh/CA-89974

CA-89974: Live migrate fails on IPv6-preferring hosts
networkd: report IPv4 address changes to xapi (as well as IPv6)

DHCP should now work well on most distros, and we can now get rid of the patch
to dhclient-script in dom0.hg (which only applies to a certain CentOS version).

Signed-off-by: Rob Hoes <rob.hoes@citrix.com>
Merge pull request #1311 from johnelse/ca-109013

CA-109013: Fix cross-pool migration and reimplement platform_version check
Merge pull request #1330 from johnelse/ca-97402

CA-97402: Add a means of disabling modules in the domainjoin-cli command
Merge pull request #1340 from robhoes/cp5153

networkd: report IPv4 address changes to xapi (as well as IPv6)