cmd/mount: reset output for 'log' package in daemon mode

[SandyXSD]

This fixes the issue that on some linux releases (e.g. Ubuntu 20.04), the go-fuse log is not printed in the juicefs.log file when running in daemon mode with -o debug.

The user reporting this issue also mentioned that the log is normal when testing on MacOS (confirmed) and early linux (kernel v.2.6).

[codecov-commenter]

Codecov Report

Base: 55.70% // Head: 55.68% // Decreases project coverage by -0.03% ⚠️

Coverage data is based on head (4f1fad3) compared to base (fcedbee).
Patch coverage: 0.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3206      +/-   ##
==========================================
- Coverage   55.70%   55.68%   -0.03%     
==========================================
  Files         142      142              
  Lines       33045    33048       +3     
==========================================
- Hits        18407    18402       -5     
- Misses      12699    12704       +5     
- Partials     1939     1942       +3     

Impacted Files	Coverage Δ
cmd/mount.go	55.01% <0.00%> (-0.34%)	⬇️
pkg/meta/tkv_mem.go	92.44% <0.00%> (-1.17%)	⬇️
pkg/meta/tkv.go	70.82% <0.00%> (-0.42%)	⬇️
pkg/meta/redis.go	66.38% <0.00%> (+0.03%)	⬆️
pkg/chunk/disk_cache.go	73.38% <0.00%> (+0.92%)	⬆️

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