Give more memory to buildbot so it can execute Soledad's large doc sync test

I included a test in Soledad test suite that will test for large doc's sync. Buildbot is complaining about lack of memory to do that:

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ERROR: test_sync_very_large_files (leap.soledad.common.tests.test_server.EncryptedSyncTestCase)
leap.soledad.common.tests.test_server.EncryptedSyncTestCase.test_sync_very_large_files
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_StringException: Traceback (most recent call last):
  File "/home/buildslave/buildslave/soledad_linux_quick/build/common/src/leap/soledad/common/tests/test_server.py", line 459, in test_sync_very_large_files
    sol1.sync()
  File "/home/buildslave/buildslave/soledad_linux_quick/build/client/src/leap/soledad/client/__init__.py", line 1110, in sync
    creds=self._creds, autocreate=True)
  File "/home/buildslave/buildslave/soledad_linux_quick/build/client/src/leap/soledad/client/sqlcipher.py", line 347, in sync
    res = self.syncer.sync(autocreate=autocreate)
  File "/home/buildslave/Virtualenvs/leap-bitmask/local/lib/python2.7/site-packages/u1db/sync.py", line 147, in sync
    self._insert_doc_from_target, ensure_callback=ensure_callback)
  File "/home/buildslave/buildslave/soledad_linux_quick/build/client/src/leap/soledad/client/target.py", line 519, in sync_exchange
    doc_json = encrypt_doc(self._crypto, doc)
  File "/home/buildslave/buildslave/soledad_linux_quick/build/client/src/leap/soledad/client/target.py", line 156, in encrypt_doc
    MAC_METHOD_KEY: MacMethods.HMAC,
  File "/home/buildslave/Virtualenvs/leap-bitmask/local/lib/python2.7/site-packages/simplejson/__init__.py", line 354, in dumps
    return _default_encoder.encode(obj)
  File "/home/buildslave/Virtualenvs/leap-bitmask/local/lib/python2.7/site-packages/simplejson/encoder.py", line 262, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/home/buildslave/Virtualenvs/leap-bitmask/local/lib/python2.7/site-packages/simplejson/encoder.py", line 340, in iterencode
    return _iterencode(o, 0)
MemoryError

We should either give more memory to buildbot or remove this test from the suite that buildbot runs.

(from redmine: created on 2014-01-20)