can't set default schema to tcp for docker host param

[lifubang]

- What I did
There is a traditional command "docker -H :2375 ps" in docker cli, but in master, it can't work now.
Is this feature removed in plan or just an error?

- How I did it
I think is an error in #1014
We need to getServerHost first, if there is an error, then go to getUnparsedServerHost

- How to verify it

- Description for the changelog
set default schema to tcp for docker host param when there is no schema

- A picture of a cute animal

[GordonTheTurtle]

Please sign your commits following these rules:
https://github.com/moby/moby/blob/master/CONTRIBUTING.md#sign-your-work
The easiest way to do this is to amend the last commit:

$ git clone -b "defaultunixschema" git@github.com:lifubang/cli.git somewhere
$ cd somewhere
$ git rebase -i HEAD~842354531984
editor opens
change each 'pick' to 'edit'
save the file and quit
$ git commit --amend -s --no-edit
$ git rebase --continue # and repeat the amend for each commit
$ git push -f

Amending updates the existing PR. You DO NOT need to open a new one.

[codecov-io]

Codecov Report

Merging #1442 into master will decrease coverage by 0.03%.
The diff coverage is 55%.

@@            Coverage Diff             @@
##           master    #1442      +/-   ##
==========================================
- Coverage    54.2%   54.16%   -0.04%     
==========================================
  Files         289      289              
  Lines       19378    19388      +10     
==========================================
- Hits        10503    10501       -2     
- Misses       8199     8213      +14     
+ Partials      676      674       -2