Change ssh option from -t to -tt

[knqyf263]

What did you implement:

Closes #359

How did you implement it:

Change ssh option from -t to -tt.
If ssh has no local tty, -tt option should be used to force pseudo-terminal allocation.

$ man ssh
 -t      Force pseudo-terminal allocation.  This can be used to execute arbitrary screen-based programs on a remote machine, which can be very useful, e.g. when implementing menu services.Multiple -t options force tty allocation, even if ssh has no local tty.

How can we verify it:

$ ./vuls scan -ssh-external

Todos:

You don't have to satisfy all of the following.

• Write tests
• Write documentation
• Check that there aren't other open pull requests for the same issue/feature
• Format your source code by make fmt
• Pass the test by make test
• Provide verification config / commands
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: YES
Is it a breaking change?: NO

[kotakanbe]

Many Thanks!