Merge ~raharper/curtin:fix/device-mapper-mpath-is-not-symlink into curtin:master

[Ryan Harper]

block-meta: device mapper partitions may be block devices not links

In some cases the multipath library may create a block device which
is not a symbolic link to the device-mapper dev[1]. Curtin expects the
symlink. Remove the non-symlink file and allow kpartx to create it.

1. https://bugzilla.redhat.com/show_bug.cgi?id=869253

[Dan Watkins (oddbloke)]

A couple of inline improvements requested, but those can follow after the RC change lands.

review: Approve

[Dimitri John Ledkov (xnox)]

review: Approve

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

PASSED: Continuous integration, rev:22172900d8090ba7f9e3110e80d9b63152d42cf7
https://jenkins.ubuntu.com/server/job/curtin-ci/58/
Executed test runs:
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-amd64/58/
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-arm64/58/
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-ppc64el/58/
    SUCCESS: https://jenkins.ubuntu.com/server/job/curtin-ci/nodes=metal-s390x/58/

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

[Ryan Harper (raharper)]

I'm doing some vmtests on the multipath scenarios, and then landing this.

[Ryan Harper (raharper)]

----------------------------------------------------------------------
Ran 156 tests in 1012.242s

OK (SKIP=20)
Wed, 22 Apr 2020 13:33:58 -0500: vmtest end [0] in 1016s

diff --git a/curtin/commands/block_meta.py b/curtin/commands/block_meta.py
index 7fbd89f..5849e3d 100644
--- a/curtin/commands/block_meta.py
+++ b/curtin/commands/block_meta.py
@@ -910,8 +910,12 @@ def partition_handler(info, storage_config):
         if multipath.is_mpath_device(disk):
             udevadm_settle()  # allow partition creation to happen
             # update device mapper table mapping to mpathX-partN
-            util.subp(['kpartx', '-v', '-a', '-s', '-p', '-part', disk])
             part_path = disk + "-part%s" % partnumber
+            # sometimes multipath lib creates a block device instead of
+            # a udev symlink, remove this and allow kpartx to create it
+            if os.path.exists(part_path) and not os.path.islink(part_path):
+                util.del_file(part_path)
+            util.subp(['kpartx', '-v', '-a', '-s', '-p', '-part', disk])
         else:
             part_path = block.dev_path(block.partition_kname(disk_kname,
                                                              partnumber))