Remove DefaultPackage() and rename a field in CrosCommand.

It looks like different commands (build, flash, deploy) will be managing
their own project objects and so there's no need for central logic for
extracting the main packages using a temporary object. Instead, we add
a convenience method MainPackages() to project.Project itself.

Two additional fixes:

- Properly catch exception due to portage_util.FindOverlays() failure.

- Rename CrosCommand.current_project into curr_project_name to make it
  clear that this is a name and not a Project instance.

BUG=brillo:173
TEST=Unit tests
TEST=Manual testing of cros {build,flash,deploy}

Change-Id: I62cd0a3ed8e282bcd0a2edd769dc02f388c3c8ea
Reviewed-on: https://chromium-review.googlesource.com/248600
Tested-by: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Bertrand Simonnet <bsimonnet@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>
5 files changed