remote-helpers: squelch python import exceptions

When the python modules are not present we get an unwanted message:

    *** prove ***
    test-bzr.sh .. Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/usr/local/buildtools/current/sitecustomize/sitecu...
        return real_import(name, globals, locals, fromlist, level)
    ImportError: No module named bzrlib
    test-bzr.sh .. skipped: skipping remote-bzr tests; bzr not available
    Files=1, Tests=0,  0 wallclock secs ( 0.03 usr  0.00 sys +  0.02 ...

Squelch that output.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
remote-helpers: move out of contrib

The remote-helpers in contrib/remote-helpers have proved to work, be
reliable, and stable. It's time to move them out of contrib, and be
distributed by default.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
remote-helpers: move tests out of contrib

They should be tested by default.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>