nydus-image: remove redundant -o short option

[changweige]

Subcommand 'unpack' introduced short option "-o" which is
redundant with global option log-level ending up with a panic

Unfortunately, github CI action didn't catch such regression :-(

INFO [utils - 93:run] - /data00/home/gechangwei/git_repo/nydus-rs/target-fusedev/debug/nydus-image create --bootstrap bootstrap_scratched --blob /data00/home/gechangwei/nydus-test-yard/blobihdgyw05 --log-level info --fs-version 6 --output-json /tmp/tmp46yv4v3_output.json /data00/home/gechangwei/nydus-test-yard/gen_rootfs_scratch
thread 'main' panicked at 'Argument short must be unique

-o is already in use', /home/gechangwei/.cargo/registry/src/mirrors.sjtug.sjtu.edu.cn-4f7dbcce21e258a2/clap-2.34.0/src/app/parser.rs:190:13

stack backtrace:
0: rust_begin_unwind
at /rustc/fe5b13d681f25ee6474be29d748c65adcd91f69e/library/std/src/panicking.rs:584:5
1: core::panicking::panic_fmt
at /rustc/fe5b13d681f25ee6474be29d748c65adcd91f69e/library/core/src/panicking.rs:143:14
2: clap::app::parser::Parser::debug_asserts

Signed-off-by: Changewei Ge [email protected]

[yqleng1987]

@changweige , a new test job has been submitted. Please wait in patience.

[yqleng1987]

@changweige , The CI test is completed, please check result:

Test Case		Test Result
merge-target-branch		✅SUCCESS
build-docker-image		✅SUCCESS
compile-nydus		✅SUCCESS
compile-ctr-remote		✅SUCCESS
compile-nydus-snapshotter		✅SUCCESS
start-nydus-snapshotter-config-containerd		✅SUCCESS
run-container-with-nydus-image		✅SUCCESS

Congratulations, your test job passed!

[hsiangkao]

I'm not sure introducing too many short options without common practice is a good idea in the long term.
My preference is to use limited common short options shared with most other mainstream program, and use long options otherwise all the time