Add a function comparing hypervisor versions

The relevance of a warning about migrating between hypervisors
of different versions depends on whether the migration is likely
to succeed or not. While it is hard to predict this in general,
this function follows best practices for Xen's current numbering
scheme.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>
Add unit test for HVVersionsLikelySafeForMigration

...by looking at the results of a few typical examples.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>
Make hypervisor check fatal

...unless force is used. This will prevent accidentally
crashing instances.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>
Add opcode Parameter pIgnoreHVVersion

This parameter will instruct instance migration to proceed in the presence
of incompatible hypervisor versions.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>
Add pIgnoreHVVersions to OpInstanceMigrate

As a parameter with default value, it will be backwards
compatible on the wire. Inside our code, however, we have
to adapt the various calls to the constructor.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>
Honor ignore_hvversions in LUInstanceMigrate

...by passing the parameter also to the tasklet.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>
Add --ignore-hvversions option

This option will be used to tell Ganeti to not error out if a
migration between nodes with incompatible hypervisor versions
is attempted.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>
Add --ignore-hvversions to gnt-instance migrate

...which simply passes on the option.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>
Add --ignore-hvversions to gnt-instance migrate man page

Describe the new option and the changed default behaviour
in the man page.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>
Document HV version checks in NEWS

The hypervisor-version check introduced an incompatible change:
Ganeti now errors out in situations where it used to warn and
then try and hope for the best. So add a not in the section on
incompatible changes.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Petr Pudlak <pudlak@google.com>