[build]: Fix comparing docker versions

[pavel-shirshov]

- What I did
Fixed issue, which caused make fails with newer docker distributions

pavelsh@pavelsh-vm:~/disk2/sonic-buildimage$ make configure PLATFORM=broadcom
+++ Making configure +++
BLDENV=stretch make -f Makefile.work configure
make[1]: Entering directory '/disk2/sonic-buildimage'
Makefile.work:52: *** SONiC requires Docker version 17.06.1 or later.  Stop.
make[1]: Leaving directory '/disk2/sonic-buildimage'
Makefile:19: recipe for target 'configure' failed
make: *** [configure] Error 

pavelsh@pavelsh-vm:~$ docker version
Client: Docker Engine - Community
 Version:           19.03.0
 API version:       1.40
 Go version:        go1.12.5
 Git commit:        aeac949
 Built:             Wed Jul 17 18:16:07 2019
 OS/Arch:           linux/amd64
 Experimental:      false

Server: Docker Engine - Community
 Engine:
  Version:          19.03.0
  API version:      1.40 (minimum version 1.12)
  Go version:       go1.12.5
  Git commit:       aeac949
  Built:            Wed Jul 17 18:14:42 2019
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.2.6
  GitCommit:        894b81a4b802e4eb2a91d1ce216b8817763c29fb
 runc:
  Version:          1.0.0-rc8
  GitCommit:        425e105d5a03fabd737a126ad93d62a9eeede87f
 docker-init:
  Version:          0.18.0
  GitCommit:        fec3683

- How I did it
Docker version is extracted as 3rd value in "server version" string. But in my docker the 3d value is "version:" not 19.03.0. So I changed the code to return last value in the string.

- How to verify it
Try to use the build system with docker version 19.03

- Description for the changelog

- A picture of a cute animal (not mandatory but encouraged)

[pavel-shirshov]

Probably it's better to fix it using
docker version --format '{{.Server.Version}}
but I don't know sinic which version it is supported.