[WIP] Adding middleware support in factory

[almahmoud]

This adds support for middleware in factory, which then gets inherited by any provider object created by this factory.

Three options to add middleware from factory:

1. Direct middleware add which will keep the same object across calls from any provider created by this factory after adding (in this example, the count will continue for all calls)

        class SomeDummyClass(object):
            count = start_count

            @intercept(event_pattern="*", priority=2499)
            def return_incremented(self, event_args, *args, **kwargs):
                self.count += 1
                return self.count

        some_obj = SomeDummyClass()
        factory.middleware.add(some_obj)

2. Middleware constructor add which will create the middleware with the class and arguments when making a new middleware manager for the provider object (in this example, count will only keep track of calls within each provider):

        class SomeDummyClassWithArgs(object):
            def __init__(self, start, increment):
                self.count = start
                self.increment = increment

            @intercept(event_pattern="*", priority=2499)
            def return_incremented(self, event_args, *args, **kwargs):
                self.count += self.increment
                return self.count

        factory = CloudProviderFactory()
        factory.middleware.add_constructor(SomeDummyClassWithArgs,
                                           start_count, increment)

and 3) adding events directly which will recreate a handler with the same callback function (bound methods will remain bound to their object)

        def return_hello(event_args, *args, **kwargs):
            return "hello"

        factory = CloudProviderFactory()
        factory.middleware.events.intercept("*", 2490, return_hello)

For all these scenarios, provider objects will inherit the events from the factory:

aws = factory.create_provider(ProviderList.AWS, {})
az = factory.create_provider(ProviderList.AZURE, {})
# Both providers will inherit all middleware/handlers added to the factory

[coveralls]

Pull Request Test Coverage Report for Build 1500

• 361 of 377 (95.76%) changed or added relevant lines in 12 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+10.1%) to 88.855%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
cloudbridge/cloud/factory.py	112	128	87.5%
<!--	Total:	361	377

Totals
Change from base Build 1470:	10.1%
Covered Lines:	7292
Relevant Lines:	7902

---

💛 - Coveralls

[codecov[bot]]

Codecov Report

Merging #195 into master will decrease coverage by 0.07%. The diff coverage is 94.42%.

@@            Coverage Diff             @@
##           master     #195      +/-   ##
==========================================
- Coverage   88.03%   87.96%   -0.08%     
==========================================
  Files          36       36              
  Lines        7775     7902     +127     
  Branches      854      868      +14     
==========================================
+ Hits         6845     6951     +106     
- Misses        594      610      +16     
- Partials      336      341       +5

Impacted Files	Coverage Δ
cloudbridge/cloud/providers/azure/services.py	88.2% <100%> (ø)	:arrow_up:
cloudbridge/cloud/providers/aws/services.py	90.09% <100%> (ø)	:arrow_up:
cloudbridge/cloud/providers/gcp/provider.py	91.95% <100%> (ø)	:arrow_up:
cloudbridge/cloud/providers/aws/provider.py	96.22% <100%> (ø)	:arrow_up:
cloudbridge/cloud/providers/mock/provider.py	100% <100%> (ø)	:arrow_up:
cloudbridge/cloud/base/provider.py	88.23% <100%> (ø)	:arrow_up:
cloudbridge/cloud/providers/openstack/provider.py	88.46% <100%> (ø)	:arrow_up:
cloudbridge/cloud/base/services.py	88.23% <100%> (ø)	:arrow_up:
cloudbridge/cloud/providers/openstack/services.py	82.08% <100%> (ø)	:arrow_up:
cloudbridge/cloud/providers/gcp/services.py	83.31% <100%> (ø)	:arrow_up:
... and 2 more

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