Merge ~raharper/curtin:fix/iscsi-dirty-disk-mode into curtin:master

[Ryan Harper]

Disable dirty_disks mode for mdadm + iscsi tests

Two issues with dirty_disk mode. First, after the early
stage runs, we need to tear down the raid array so we can
disconnect the iscsi devices, second even when that is done
there is a bug in mdadm version in Artful and Bionic which
prevents successful testing (LP: #1753786)

[Server Team CI bot (server-team-bot)]

PASSED: Continuous integration, rev:3ceb51697399b64f55a80da6663b7cb3c7f25545
https://jenkins.ubuntu.com/server/job/curtin-ci/863/
Executed test runs:
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-amd64/863
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-arm64/863
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-ppc64el/863
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-s390x/863

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review: Approve (continuous-integration)

[Scott Moser (smoser)]

review: Needs Fixing

[Ryan Harper (raharper)]

Added comment to the line in the test-case file referencing the bug.

[Server Team CI bot (server-team-bot)]

PASSED: Continuous integration, rev:9a0469c92371e632480d6f991d50516d5eda75c6
https://jenkins.ubuntu.com/server/job/curtin-ci/865/
Executed test runs:
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-amd64/865
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-arm64/865
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-ppc64el/865
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-s390x/865

Click here to trigger a rebuild:
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review: Approve (continuous-integration)

diff --git a/tests/vmtests/test_mdadm_iscsi.py b/tests/vmtests/test_mdadm_iscsi.py
index 9c028dc..3c8e6ef 100644
--- a/tests/vmtests/test_mdadm_iscsi.py
+++ b/tests/vmtests/test_mdadm_iscsi.py
@@ -9,6 +9,7 @@ import textwrap
 
 class TestMdadmIscsiAbs(TestMdadmAbs, TestBasicIscsiAbs):
     interactive = False
+    dirty_disks = False  # LP: 1753786
     iscsi_disks = [
         {'size': '5G', 'auth': 'user:passw0rd'},
         {'size': '5G', 'auth': 'user:passw0rd', 'iauth': 'iuser:ipassw0rd'},