Fix GetStatus(), GetTable() to return multi-line tables

[trgill]

fixes #39833

Device mapper target tables may have multiple lines. When the table has
multiple lines, it is required that dm_get_next_target(ptr) be called
until the returned pointer is Nil. Examples of using dm_get_next_target()
can be found in libdm/dm-tools/dmsetup.c

- What I did

Update GetStatus and GetTable to fetch and return more than just the first
line of the DM table.

- How I did it

Added TargetLine type to represent a single line of the DM table. An
array of TargetLine is used to return the full table.

Update getThinPoolDataMetaMajMin() to hanle an array of TargetLine.

- How to verify it

Create a multi-line DM target
Call GetStatus() and GetTable() with/without the fix

- Description for the changelog
Fix GetStatus(), GetTable() to return multi-line tables

[thaJeztah]

/cc @rhvgoyal ptal

[thaJeztah]

ping @kolyshkin PTAL

[thaJeztah]

@trgill looks like build is failing;

# github.com/docker/docker/pkg/devicemapper
pkg/devicemapper/devmapper.go:558:29: syntax error: mixed named and unnamed function parameters

[kolyshkin]

@trgill this code is not compileable, please fix:

kir@kd:~/go/src/github.com/docker/docker$ ./hack/make.sh dynbinary

Removing bundles/

---> Making bundle: dynbinary (in bundles/dynbinary)
Building: bundles/dynbinary-daemon/dockerd-dev
GOOS="" GOARCH="" GOARM=""
# github.com/docker/docker/pkg/devicemapper
pkg/devicemapper/devmapper.go:562:3: too many arguments to return
	have (number, number, string, string, error)
	want ([]TargetLine, error)
pkg/devicemapper/devmapper.go:566:3: too many arguments to return
	have (number, number, string, string, error)
	want ([]TargetLine, error)
pkg/devicemapper/devmapper.go:572:3: too many arguments to return
	have (number, number, string, string, error)
	want ([]TargetLine, error)
pkg/devicemapper/devmapper.go:576:3: too many arguments to return
	have (number, number, string, string, error)
	want ([]TargetLine, error)
pkg/devicemapper/devmapper.go:618:10: tl.start undefined (type *TargetLine has no field or method start, but does have Start)
pkg/devicemapper/devmapper.go:618:20: tl.length undefined (type *TargetLine has no field or method length, but does have Length)
pkg/devicemapper/devmapper.go:618:31: tl.targetType undefined (type *TargetLine has no field or method targetType, but does have TargetType)
pkg/devicemapper/devmapper.go:618:46: tl.params undefined (type *TargetLine has no field or method params, but does have Params)

[trgill]

@kolyshkin fixed.

Looks like a couple unit tests TestDevmapperReduceLoopBackSize and TestDevmapperIncreaseLoopBackSize are failing. I'll have a look to see if I introduced the problem.

[trgill]

I don't think the test failures are related to this change. The log entries after the failures indicate:

[2019-09-30T21:38:12.450Z] time="2019-09-30T21:36:38Z" level=error msg="Udev sync is not supported. This will lead to data loss and unexpected behavior. Install a more recent version of libdevmapper or select a different storage driver. For more information, see https://docs.docker.com/engine/reference/commandline/dockerd/#storage-driver-options" storage-driver=devicemapper

[thaJeztah]

The devicemapper storage-driver was deprecated, and has been removed, so closing issues related to this storage-driver. See;

• Deprecate "devicemapper" storage driver, and add warning #38017
• Remove deprecated devicemapper storage driver #43637