*: support recover relay log file with a subset of metadata (#530)

[csuzhangxc]

cherry-pick #530 to release-1.0

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What problem does this PR solve?

fix #443 , this should be release under v1.0.4.

What is changed and how it works?

• support recover relay log file with a subset of metadata

  • check whether the metadata is a subset of the relay log file

• also update go-mysql to fix GTIDSet.Equal.

Check List

Tests

• Unit test
• Integration test

Code changes

• Has exported variable/fields change
• Has persistent data change

Side effects

• Increased code complexity

Related changes

• Need to cherry-pick to the release branch
• Need to be included in the release note

[csuzhangxc]

/run-all-tests tidb=release-3.0

[lichunzhu]

LGTM

[WangXiangUSTC]

LGTM

[codecov]

Codecov Report

Merging #534 into release-1.0 will decrease coverage by 0.0359%.
The diff coverage is 60.0000%.

@@                 Coverage Diff                 @@
##           release-1.0       #534        +/-   ##
===================================================
- Coverage      57.3194%   57.2835%   -0.0360%     
===================================================
  Files              161        161                
  Lines            16661      16654         -7     
===================================================
- Hits              9550       9540        -10     
- Misses            6167       6172         +5     
+ Partials           944        942         -2