bitbake: toaster: bldcontrol models Add a cancelling state the BuildRequest

To accurately reflect the state of a build request we also need a
cancelling state. This is set when we've started a build and then for
whatever reason cancel it, cancelling is not instantaneous so we have
this state to indicate that a cancel is in progress.

Also add a state transition guard. As the state of a BuildRequest can
currently be modified by three processes; Toastergui,
Runbuilds/bldcontrol and the buildinofhelper we cannot say for sure
which process will be running at the time of cancellation so in order to
avoid one of these processes making an incorrect transition only allow
transitions of state to increase.

e.g. CREATED -> QUEUED -> INPROGRESS
And to ignore such requested changes such as
INPROGRESS -> CREATED

(Bitbake rev: 449598c8e6be75bd0c9d59e7bdf859d1d6f83858)

Signed-off-by: Michael Wood <michael.g.wood@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/toaster/bldcontrol/migrations/0003_add_cancelling_state.py

@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('bldcontrol', '0002_auto_20160120_1250'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='buildrequest',
+            name='state',
+            field=models.IntegerField(default=0, choices=[(0, b'created'), (1, b'queued'), (2, b'in progress'), (3, b'completed'), (4, b'failed'), (5, b'deleted'), (6, b'cancelling'), (7, b'archive')]),
+        ),
+    ]