vmm: support readonly option of volume #1182

Job	Run time
tests (vmm/sandbox, --all-features)	3m 34s
checks (vmm/sandbox, --all-features)	4m 33s
tests (vmm/task, --all-features)	2m 45s
checks (vmm/task, --all-features)	3m 48s
tests (shim, --all-features)	2m 34s
checks (shim, --all-features)	3m 57s
tests (quark, --all-features)	2m 32s
checks (quark, --all-features)	3m 36s
tests (runc, --all-features)	2m 40s
checks (runc, --all-features)	3m 48s
tests (wasm, --features=wasmedge, 0.13.5)	3m 31s
checks (wasm, --features=wasmedge, 0.13.5)	4m 32s
tests (wasm, --features=wasmtime)	3m 52s
checks (wasm, --features="wasmedge, wasmedge_wasi_nn", 0.13.5)	4m 32s
checks (wasm, --features=wasmtime)	4m 28s
	54m 42s

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