Context aware completion for ssh command

[rebrendov]

Solves #3416.

Changes for zsh were tested on ArchLinux machine and changes for bash were tested on ArchLinux and Ubuntu Server machines.

For bash had to copy-paste _fzf_complete call from _fzf_host_completion to _fzf_ssh_completion to make sure that _fzf_ssh_completion_post is called.

[rebrendov]

Seems that new logic broke the tests. I'll try to fix it.

[rebrendov]

Ok, made sure make docker-test is passing.

[junegunn]

I tried to simplify the code and make both implementations as similar as possible.

• Prepend the user part to the input so the post function is not required
• [bash] Remove the reliance on $prefix variable across the functions
• [bash] Fix the bug where the part after @ is lost. e.g. ssh jg@10**<tab>
• [zsh] Update telnet completion to receive the same set of hosts as ssh

Let me know what you think.

[junegunn]

Merged with a test case. Thanks.

[rebrendov]

Sorry, I forgot to send a comment. The simplified code looks great. Thank you for the useful tool!