Connections leaks in resource manager

[xuzifu666]

What this PR does:

Which issue(s) this PR fixes:

Fixes #1008

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 61.64%. Comparing base (afb8650) to head (f3ffd85).

Files with missing lines	Patch %	Lines
pkg/datasource/sql/xa_resource_manager.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1011      +/-   ##
==========================================
- Coverage   61.65%   61.64%   -0.01%     
==========================================
  Files         213      213              
  Lines       13054    13056       +2     
==========================================
  Hits         8049     8049              
- Misses       4481     4483       +2     
  Partials      524      524              

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[0x-infinity]

LGTM