xe host-apply-edition: avoid race in error reporting

When host.apply_edition raises a license_checkout_error exception, we look at
the recent alerts (messages) to find out the reason for the failure. We seem to
currently miss such an alert every now and then, possibly due to rounding
errors in the used timestamp.  Make this less likely by subtracting a second.

Signed-off-by: Rob Hoes <rob.hoes@citrix.com>
xe host-apply-edition: cleanup alert after processing

Signed-off-by: Rob Hoes <rob.hoes@citrix.com>
CA-145689: xe host-apply-edition: take into account new v6_license_server_version_obsolete alert

Signed-off-by: Rob Hoes <rob.hoes@citrix.com>
Merge pull request #1957 from robhoes/lic

Improvements to 'xe host-apply-edition'