Added support for Spec and Post-Install

[akritkbehera]

This adds support for generating spec files using rpmBuild if --generate-rpm flag is used while building packages.

[akritkbehera]

Hi @smuzaffar.
I have implemented the RPM dependency resolution in the file
https://github.com/akritkbehera/bits-org/blob/f5bb4ac882b08666f22b35849dfeff18612a800b/bits_helpers/dependency.py
and we implement the checking towards at the end of build.py
If you could take a look at it.

[smuzaffar]

@akritkbehera , I would suggest to dump rpm provides and requires here and then run dependency checking ( by finding all its requires from its dependency packages). This way dependency checking can be run in parallel and once we are done here then package should be ready to be uploaded.

[smuzaffar]

@akritkbehera , I would suggest to add a %post section too which can just call the relocation script . This way we can have fully working RPM package