qidoc build: improve argument parsing
qidoc build: improve argument parsing

* Do not use cwd if --work-tree is used
* Do not try to build all if current project can't be guessed
* Build all when no argument is given *only* at the root of the worktree

Change-Id: Ib684786f4e85dea890e4294d9e661942951f53f8
Reviewed-on: http://gerrit.aldebaran.lan:8080/1024
Reviewed-by: llec <42f1a1c02cacc0f5b0188f0127ea77bedfdcf21a@aldebaran-robotics.com>
Tested-by: llec <42f1a1c02cacc0f5b0188f0127ea77bedfdcf21a@aldebaran-robotics.com>

aldebaran/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild