Add unit tests, remove mobile hub service role

[UnleashedMind]

Issue #, if available:

Description of changes:

• add unit tests for appsync feature related code
• remove mobile hub service role related code

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-io]

Codecov Report

Merging #111 into master will increase coverage by 17.95%. The diff coverage is 53.84%.

@@             Coverage Diff             @@
##           master     #111       +/-   ##
===========================================
+ Coverage   62.91%   80.87%   +17.95%     
===========================================
  Files          85       85               
  Lines        5666     5688       +22     
  Branches      895      910       +15     
===========================================
+ Hits         3565     4600     +1035     
+ Misses       1756      929      -827     
+ Partials      345      159      -186

Impacted Files	Coverage Δ
...perations/appsync-operations/ops-appsync-update.js	77.87% <ø> (+68.9%)	:arrow_up:
lib/aws-operations/aws-config-manager.js	85.58% <ø> (+4.38%)	:arrow_up:
...perations/appsync-operations/ops-appsync-delete.js	80.95% <ø> (+34.52%)	:arrow_up:
lib/utils/awsmobilejs-constant.js	100% <ø> (ø)	:arrow_up:
lib/aws-operations/aws-exception-handler.js	100% <ø> (ø)	:arrow_up:
lib/backend-operations/ops-cloud-api.js	59.54% <0%> (-2.86%)	:arrow_down:
lib/backend-create.js	89.58% <0%> (-3.9%)	:arrow_down:
lib/backend-operations/ops-appsync.js	84.05% <100%> (+13.76%)	:arrow_up:
...rations/appsync-operations/ops-appsync-retrieve.js	82.03% <100%> (+69.39%)	:arrow_up:
lib/feature-operations/scripts/appsync-ops.js	71.76% <56.86%> (+47.76%)	:arrow_up:
... and 16 more

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