Add --archive option to init to sync using git archive

This significantly reduces sync time and used brandwidth as only
a tar of each project's revision is checked out, but git is not
accessible from projects anymore.

This is relevant when git is not needed in projects but sync
speed/brandwidth may be important like on CI servers when building
several versions from scratch regularly for example.

Archive is not supported over http/https.

Change-Id: I48c3c7de2cd5a1faec33e295fcdafbc7807d0e4d
Signed-off-by: Julien Campergue <julien.campergue@parrot.com>

repo

@@ -180,6 +180,10 @@ group.add_option('--reference',
 group.add_option('--depth', type='int', default=None,
                  dest='depth',
                  help='create a shallow clone with given depth; see git clone')
+group.add_option('--archive',
+                 dest='archive', action='store_true',
+                 help='checkout an archive instead of a git repository for '
+                      'each project. See git archive.')
 group.add_option('-g', '--groups',
                  dest='groups', default='default',
                  help='restrict manifest projects to ones with specified '