Refactor ForwardingJob class and fix few issues

[shafreenAnfar]

Hi All,

This PR does the $subject and in the process I have fixed two issues as well.

Programmers spend more time to reading code and less time on writing code. Therefore, it is needless to say that having readable code is essential in any project. ForwardingJob class was actually the opposite of this (forgive me for saying this) and it is very hard to read the code do new modification. Making the code vulnerable for regression issues.

Therefore, I have refactored the code starting the basic principle of functions doing one and only one thing. In the processes I have moved some variables into class variables as actually control the state of the ForwadingJob. Also, code abstraction done in a way that, reader starts with the highest abstraction of the concept and then drill down to more granular abstractions. This is similar to news-paper metaphor. Also, all the functions follow vertical affinity and therefore closely related functions are placed next to other.

Please note that after the refactor I have re-tested all the scenarios such as,

Out Only Scenario

• Success scenario
• Retry scenario
• Max delivery scenario
• Max delivery drop scenario
• Invoking Deactivate scenario

Response Scenario

• Success scenario
• Retry scenario
• Retry on application level failure scenario
• Invoking reply sequence scenario
• Invoking fault sequence scenario
• Invoking deactivate sequence scenario
• Max delivery attempt scenario
• Max delivery drop scenario

Along with this I have fixed below two bugs,

https://issues.apache.org/jira/browse/SYNAPSE-1120
https://issues.apache.org/jira/browse/SYNAPSE-1121

[isudana]

Thanks Shafreen, I will take time and review the PR.