core: Move Guid constants

Moved the constant Guid instances to be initialized after Guid's
static fields to ensure that these Guids aren't partly initialized.

This patch addresses the FindBugs wanring
SI_INSTANCE_BEFORE_FINALS_ASSIGNED - "Static initializer for
org.ovirt.engine.core.compat.Guid creates instance before all static
final fields assigned"

Change-Id: If239587d8bddba89e19253ec1e147ef770b60e85
Signed-off-by: Allon Mureinik <amureini@redhat.com>
core: Remove null check from Guid.equals(Object)

Since (null instanceof anyObject) always returns false anyway, it's
redundant to explicitly check for nulls.

Change-Id: Ia8a5a0ba443a7a0d1c8769ff73a723fb3be0f801
Signed-off-by: Allon Mureinik <amureini@redhat.com>
core: Append chars instead of Strings in Guid

Append '-' instead of "-" as StringBuilder.append(char) has slightly
better performance than StringBuilder.append(String).

Change-Id: Ib9dacce56a06d92307763c7f9ad5f59723e82e04
Signed-off-by: Allon Mureinik <amureini@redhat.com>