Convert GRPC Integration tests to run as UT

[avanaur]

Changes

Convert GRPC Integration tests to component tests runnable as unit tests.

The component tests uses an SQLite as in-memory DB.

The variable isIntegrationTests is removed but the tag integration_tests is kept for conductor RPC setup (although this seems not completely setup anymore).

Minor change on some GORM fields to use default:current_timestamp instead of default:now() to work with SQLite.

Fixes

Resolves #607

Tests

Tasks to complete before merging PR:

• Ensure system tests are passing. If not Run them manually to check for any regressions 📋
• Do any new system tests need added to test this change? do any existing system tests need updated? If so create a PR at 0chain/system_test
• Merge your system tests PR to master AFTER merging this PR

Associated PRs (Link as appropriate):

• 0chain:
• gosdk:
• system_test:
• zboxcli:
• zwalletcli:
• Other: ...

[codecov-commenter]

Codecov Report

Merging #747 (b8561db) into staging (28ea8c0) will increase coverage by 5.99%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           staging     #747      +/-   ##
===========================================
+ Coverage    24.01%   30.01%   +5.99%     
===========================================
  Files           68       68              
  Lines         7653     7653              
===========================================
+ Hits          1838     2297     +459     
+ Misses        5548     5014     -534     
- Partials       267      342      +75     

Flag	Coverage Δ
Unit-Tests	30.01% <ø> (+5.99%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...o/0chain.net/blobbercore/reference/collaborator.go	0.00% <ø> (ø)
.../0chain.net/blobbercore/reference/commitmetatxn.go	0.00% <ø> (ø)
code/go/0chain.net/blobbercore/reference/ref.go	0.00% <ø> (ø)
...e/go/0chain.net/blobbercore/reference/shareinfo.go	0.00% <ø> (ø)
code/go/0chain.net/blobbercore/handler/handler.go	64.14% <0.00%> (+7.07%)	⬆️
.../go/0chain.net/blobbercore/handler/grpc_helpers.go	78.04% <0.00%> (+7.31%)	⬆️
...et/blobbercore/handler/object_operation_handler.go	43.03% <0.00%> (+13.37%)	⬆️
...o/0chain.net/blobbercore/handler/handler_common.go	32.65% <0.00%> (+15.30%)	⬆️
.../0chain.net/blobbercore/handler/storage_handler.go	39.30% <0.00%> (+15.53%)	⬆️
...ain.net/blobbercore/handler/grpc_commit_handler.go	64.00% <0.00%> (+64.00%)	⬆️
... and 2 more

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[peterlimg]

lgtm