refactor label name to reduce the length of label

[cheyang]

Ⅰ. Describe what this PR does

Ⅱ. Does this pull request fix one issue?

Ⅲ. List the added test cases (unit test/integration test) if any, please explain if no tests are needed.

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-io]

Codecov Report

Merging #696 (e8f4cd9) into master (96d8cf1) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master     #696   +/-   ##
=======================================
  Coverage   16.81%   16.81%           
=======================================
  Files          67       67           
  Lines        2943     2943           
=======================================
  Hits          495      495           
  Misses       2397     2397           
  Partials       51       51           

Impacted Files	Coverage Δ
pkg/ddc/alluxio/label.go	10.00% <ø> (ø)
pkg/ddc/alluxio/shutdown.go	0.00% <0.00%> (ø)

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