sync: catch exceptions when connecting to the manifest server

When connecting to the manifest server, exceptions can occur but
are not caught, resulting in the repo sync exiting with a python

Add handling of the following exceptions:

- IOError, which can be raised for example if the manifest server
URL is malformed.
- xmlrpclib.ProtocolError, which can be raised if the connection
to the manifest server fails with HTTP error.
- xmlrpclib.Fault, which can be raised if the RPC call fails for
some other reason.

Change-Id: I3a4830aef0941debadd515aac776a3932e28a943
1 file changed