test: add e2e test cases for limit-count plugin

[tokers]

Please answer these questions before submitting a pull request

• Why submit this pull request?

• Bugfix

• New feature provided

• Improve performance

• Backport patches

• Related issues

---

Bugfix

• Description

• How to fix?

---

New feature or improvement

• Describe the details and related test reports.

---

Backport patches

• Why need to backport?

• Source branch

• Related commits and pull requests

• Target branch

[codecov-io]

Codecov Report

Merging #328 (1552db1) into master (06e2b35) will decrease coverage by 0.48%.
The diff coverage is n/a.

❗ Current head 1552db1 differs from pull request most recent head 566e705. Consider uploading reports for the commit 566e705 to get more accurate results

@@            Coverage Diff             @@
##           master     #328      +/-   ##
==========================================
- Coverage   42.65%   42.17%   -0.49%     
==========================================
  Files          40       39       -1     
  Lines        3418     3417       -1     
==========================================
- Hits         1458     1441      -17     
- Misses       1801     1815      +14     
- Partials      159      161       +2     

Impacted Files	Coverage Δ
pkg/apisix/cluster.go	28.44% <0.00%> (-5.97%)	⬇️
pkg/apisix/route.go	41.29% <0.00%> (-1.94%)	⬇️
test/e2e/e2e.go

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 06e2b35...566e705. Read the comment docs.