implement file ignore in the profile enable process

[chanwit]

This PR makes the profile enable command to uses contents of the .wksctlignore file, if exists on the top most directory of the profile, to filter out unneeded files.

What does this PR do:

1. detect .wksctlignore at the top level directory of the profile.
2. use each line of the .wksctlignore file to do git rm.
3. amend the previous commit (done by git subtree add)

A test case to test the processing of .wksctlignore is included.

[chanwit]

cc @palemtnrider
This is the PR to process the ignore file for wskctl.

[mflendrich]

It feels to me that wksctl in wksctlignore refers to our tool in an overly specific way. It is not impossible that we have another tool (other than wksctl) in the future that deals with profiles, for example.

Unless we're already committed to calling this .wksctlignore, I suggest renaming to .profileignore.

[chanwit]

@mflendrich basically yes, it is very specific to wksctl. Let me explain by referring to this example profile:
https://github.com/chanwit/eks-quickstart-app-dev

In the above profile, there are two ignore files .eksctlignore and .wksctlignore.
Each of them contains a set of file needs to be removed by each tool.

This is by design to make a single profile repo works on both eksctl and wksctl.
Thinking of this as a situation that we have .circleci, .travis.yaml and .drone.yaml files on a git repo to allow each CI to independently process our repo (in its own way).

[fbarl]

Very nice and clean PR, code LGTM! 👍

[chanwit]

Thank you @mflendrich and @fbarl for your kindly reviews!