cluster/import: read enable_binlog from inventory

[AstroProfundis]

What problem does this PR solve?

The enable_binlog switch in ansible inventory is not imported.

What is changed and how it works?

Read the variable and set tidb config if it is set to True.

Release Note

Supporting import clusters with binlog enabled

[lucklove]

LGTM

[july2993]

LGTM

[codecov-commenter]

Codecov Report

Merging #652 into master will increase coverage by 0.63%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #652      +/-   ##
==========================================
+ Coverage   56.71%   57.34%   +0.63%     
==========================================
  Files         242      243       +1     
  Lines       17469    17512      +43     
==========================================
+ Hits         9908    10043     +135     
+ Misses       6265     6167      -98     
- Partials     1296     1302       +6     

Flag	Coverage Δ
#coverage	57.34% <ø> (+0.63%)	⬆️

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

Impacted Files	Coverage Δ
...c/github.com/pingcap/tiup/pkg/cluster/spec/spec.go	90.94% <0.00%> (-2.62%)	⬇️
...hub.com/pingcap/tiup/pkg/cluster/ansible/import.go	48.07% <0.00%> (-1.93%)	⬇️
...m/pingcap/tiup/components/cluster/command/check.go	81.63% <0.00%> (-0.50%)	⬇️
...src/github.com/pingcap/tiup/pkg/cluster/manager.go	70.37% <0.00%> (-0.20%)	⬇️
....com/pingcap/tiup/pkg/cluster/spec/spec_manager.go	67.50% <0.00%> (-0.15%)	⬇️
...c/github.com/pingcap/tiup/pkg/cluster/api/dmapi.go	61.31% <0.00%> (ø)
....com/pingcap/tiup/pkg/cluster/operation/destroy.go	54.48% <0.00%> (ø)
...com/pingcap/tiup/pkg/cluster/spec/server_config.go	65.87% <0.00%> (ø)
....com/pingcap/tiup/pkg/cluster/clusterutil/retry.go
...ub.com/pingcap/tiup/pkg/cliutil/prepare/prepare.go
... and 7 more

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