Rename Ec2Base#connection to Ec2Base#ec2_connection

[kvivek1115]

Describe the Enhancement:

There is a conflict of connection method while we inheriting the class Chef::Knife::Bootstrap class into Ec2ServerCreate both having connection method one for aws connection came from module Ec2Base another for bootstrap node connection from the train.
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Describe the Need:

Now we are going to change design implementation so both connection methods are required.
For now, I can only think of renaming Ec2Base module connection method to ec2_connection

[dheerajd-msys]

Closing as it merged in #583