Changed spec deletion order according to dependency

[blackfly19]

Description

Changed spec deletion order according to dependency.

Which issue(s) this PR fixes:

Testing

Tested using this example. https://github.com/fission/examples/tree/master/spec-example/hello-spec-exmaple

Sample Output:

• fission spec destroy

Deleted Function default/hello
Deleted Package default/hello-pkg
Deleted Environment default/python-27

Checklist:

• I ran tests as well as code linting locally to verify my changes.
• I have done manual verification of my changes, changes working as expected.
• I have added new tests to cover my changes.
• My changes follow contributing guidelines of Fission.
• I have signed all of my commits.

[codecov]

Codecov Report

Merging #2344 (0413781) into master (3ac1881) will not change coverage.
The diff coverage is n/a.

❗ Current head 0413781 differs from pull request most recent head 8aa85ba. Consider uploading reports for the commit 8aa85ba to get more accurate results

@@           Coverage Diff           @@
##           master    #2344   +/-   ##
=======================================
  Coverage   18.79%   18.79%           
=======================================
  Files          56       56           
  Lines        6295     6295           
=======================================
  Hits         1183     1183           
  Misses       5028     5028           
  Partials       84       84           

Flag	Coverage Δ
unittests	18.79% <ø> (ø)

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