Add helpers to create per-aggregate filters

This patchset introduce a new file of utility methods
to deal with aggregate metadata.
As well it updates related filters to use this new logic.
* AggregateRamFilter
* AggregateCoreFilter,
* AggregateTypeAffinityFilter

Closes-Bug: #1301340
Change-Id: I5e4aebe9e61cfbdc7b9e6b5de0788fc6670eb936
VMware: Fix memory leaks caused by caches

Using suds objects as keys for the DatastoreBrowser cache is incorrect
because they don't implement __eq__ and __hash__ for the VIM types.
This always results in cache miss and the cache grows with every spawn()
operation.

This patch fix this by using the 'value' property (which is string) of
the MoRef as key.

Change-Id: I2bcaf87e733d51055566aee41bb0a7e254027ba9
Closes-Bug: 1316433
Merge "Add helpers to create per-aggregate filters"
Merge "VMware: Fix memory leaks caused by caches"