Generate GO bindings for vCenter Storage Policy Based Management (SPBM)

[BaluDontu]

I have a PR out in vmware/govmomi repo that generates GO bindings for SPBM- vmware/govmomi#708

The PR just contains generated GO binding files and not the code which I wrote to generate the bindings.

[BaluDontu]

Also included the code I have written to generate the GO bindings as part of PR posted above. These changes will be used Doug, to make the govmomi/gen/ scripts more generic to be used by different end points.

[BaluDontu]

I now have the PBM bindings and the 3 wrapper functions for PBM merged in govmomi.
Following have been achieved so far,

1. QueryProfile
2. RetrieveContent
3. CheckRequirements

Also added a new endpoint for pbm - /pbm/sdk.

[BaluDontu]

With the help of Doug, I was able to write the wrapper functions and check in those changes - vmware/govmomi#711