test: add short flag for store unit test because it's using dockertest for integration tests

[swallowstalker]

try to solve issue #354 so that people using Guardian will have options of disabling store package test which uses dockertest that requires connecting to /var/run/docker.sock

$ go test -count=1 -race -v -short github.com/odpf/guardian/internal/store/postgres
=== RUN   TestActivityRepository
    activity_repository_test.go:32:
--- SKIP: TestActivityRepository (0.00s)
=== RUN   TestAppealRepository
    appeal_repository_test.go:393:
--- SKIP: TestAppealRepository (0.00s)
=== RUN   TestApprovalRepository
    approval_repository_test.go:30:
--- SKIP: TestApprovalRepository (0.00s)
=== RUN   TestGrantRepository
    grant_repository_test.go:34:
--- SKIP: TestGrantRepository (0.00s)
=== RUN   TestPolicyRepository
    policy_repository_test.go:208:
--- SKIP: TestPolicyRepository (0.00s)
=== RUN   TestProviderRepository
    provider_repository_test.go:381:
--- SKIP: TestProviderRepository (0.00s)
=== RUN   TestResourceRepository
    resource_repository_test.go:424:
--- SKIP: TestResourceRepository (0.00s)
PASS
ok  	github.com/odpf/guardian/internal/store/postgres	0.691s

[coveralls]

Pull Request Test Coverage Report for Build 4245835458

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 75.061%

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Totals
Change from base Build 4230034365:	0.0%
Covered Lines:	7714
Relevant Lines:	10277

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💛 - Coveralls