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>

manifest_xml.py

@@ -329,6 +329,10 @@ class XmlManifest(object):
   def IsMirror(self):
     return self.manifestProject.config.GetBoolean('repo.mirror')
 
+  @property
+  def IsArchive(self):
+    return self.manifestProject.config.GetBoolean('repo.archive')
+
   def _Unload(self):
     self._loaded = False
     self._projects = {}