IL-250 Look for docker cli next to the current executable

[mat007]

What I did

If com.docker.cli is not in the path, look for it next to the current running executable.

Related issue

Fixes #754

To test:

1. with Docker Desktop installed make sure to move com.docker.cli out of the path by doing e.g. mv /Applications/Docker.app/Contents/Resources/bin/com.docker.cli /Applications/Docker.app/Contents/Resources/bin/com.docker.cli_
2. build and run ./bin/docker version, it should error out with

$ ./bin/docker version
exec: "com.docker.cli": executable file not found in $PATH
Current PATH : (…)

3. copy com.docker.cli into ./bin:

cp /Applications/Docker.app/Contents/Resources/bin/com.docker.cli_ ./bin/com.docker.cli

4. re-run:

$ ./bin/docker version
Client:
Cloud integration: 2.0.0-beta.4-1-g949062d5
Version:           20.10.7
API version:       1.41
(̣̣…)

(not mandatory) A picture of a cute animal, if possible in relation with what you did

[ndeloof]

@mat007 OSS contributor have to sign-off commits (git commit -s)

[mat007]

Oh sorry! Fixed.