add more unit tests for scan file

[kanchwala-yusuf]

adding unit test for file scan API endpoint

[codecov]

Codecov Report

Merging #261 into terrascan-v1.0 will increase coverage by 17.34%.
The diff coverage is 70.00%.

@@                 Coverage Diff                 @@
##           terrascan-v1.0     #261       +/-   ##
===================================================
+ Coverage           54.38%   71.72%   +17.34%     
===================================================
  Files                  20       21        +1     
  Lines                 456      474       +18     
===================================================
+ Hits                  248      340       +92     
+ Misses                186      107       -79     
- Partials               22       27        +5     

Impacted Files	Coverage Δ
pkg/http-server/file-scan.go	71.15% <59.09%> (+71.15%)	⬆️
pkg/http-server/helpers.go	100.00% <100.00%> (ø)
pkg/iac-providers/terraform/v12/convert.go	75.35% <0.00%> (+24.64%)	⬆️
pkg/runtime/executor.go	88.88% <0.00%> (+44.44%)	⬆️