nydus-image: modify compact interface

[SToPire]

This commit uses compact parameter directly insteadof compact config file in the cli interface. It also fix a bug where chunk key for ChunkWrapper::Ref is not generated correctly.

Types of changes

What types of changes does your PullRequest introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation Update (if none of the other choices apply)

[codecov]

Codecov Report

Attention: Patch coverage is 1.36986% with 72 lines in your changes missing coverage. Please review.

Project coverage is 61.23%. Comparing base (a4683ba) to head (eacb9f5).

Files with missing lines	Patch %	Lines
src/bin/nydus-image/main.rs	0.00%	63 Missing ⚠️
builder/src/compact.rs	10.00%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1631      +/-   ##
==========================================
- Coverage   61.28%   61.23%   -0.05%     
==========================================
  Files         146      146              
  Lines       48156    48189      +33     
  Branches    46123    46156      +33     
==========================================
- Hits        29512    29509       -3     
- Misses      17085    17119      +34     
- Partials     1559     1561       +2     

Files with missing lines	Coverage Δ
builder/src/lib.rs	64.66% <ø> (ø)
builder/src/compact.rs	79.90% <10.00%> (-0.43%)	⬇️
src/bin/nydus-image/main.rs	0.62% <0.00%> (-0.01%)	⬇️

... and 2 files with indirect coverage changes