Synnefo

Support timeout in ObjectPool.get(), fix tests

Support optional timeout argument in ObjectPool.get(),
if supported by the underlying Semaphore implementation.

Implement command-line argument for ObjectPool unit tests to run
inside gevent monkey-patched environment.

Add ObjectPool class in synnefo.lib

Add ObjectPool class in synnefo.lib.
The ObjectPool class is an abstract pool of objects,
based on Semaphore locks, as provided by the threading
package.

Tested to work with a gevent-monkey-patched threading package.
Uncomment the relevant lines in pool/tests.py to test with greenlet...

Implement Singleton pattern

Implement Singleton pattern inside synnefo.lib.singleton.

Whenever a class inherits from ArgBasedSingleton,
attempts to call the class do not always create a new
class instance, but return pre-existing, already made objects.
...

Pass tags to ganeti CreateNetwork RAPI call

Merge branch 'simplequotas' into queues+minor_net