2a733418 (slaprunner: replaces dropbear by openssh) switched slaprunner
sshd from dropbear to openssh (thanks for it once again) and used
ForceCommand to imitate login shell to be partitions `${bash:location}/bin/bash -l`.

For case when original ssh command is explicitly provided
("$SSH_ORIGINAL_COMMAND" is not empty) the code there tries to just
execute what was provided by caller.

However the reexecution is not completely correct as for cases when
origin command contains some quoting, 1 level of quotes is removed.

The case when I hit this in practice is git access to repositories over
ssh. When git wants to e.g. clone a repository it runs `git-upload-pack
quoted-path-to-repo.git` and fails this way:

```
$ GIT_TRACE=1 git clone ssh://host1/~/B.git
19:28:23.558858 git.c:350               trace: built-in: git 'clone' 'ssh://host1/~/B.git'
Cloning into 'B'...
19:28:23.572994 run-command.c:336       trace: run_command: 'ssh' 'host1' 'git-upload-pack '\''~/B.git'\'''
fatal: ''~/B.git'' does not appear to be a git repository
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.
```

Quoting SSH_ORIGINAL_COMMAND and evaluating it completely via eval fixes this.

/cc @Nicolas, @alain.takoudjou