add mkfs for extfs and overlaybd-apply

[liulanzheng]

What this PR does / why we need it:

add mkfs for extfs and overlaybd-apply/create

• add a simple mkfs implementation with specific parameters
• produce reproducible result with fixed uuid and hash seed
• add --mkfs flag for overlaybd-apply/create, which do mkfs before apply data / after create

Please check the following list:

• Does the affected code have corresponding tests, e.g. unit test, E2E test?
• Does this change require a documentation update?
• Does this introduce breaking changes that would require an announcement or bumping the major version?
• Do all new files have an appropriate license header?

[yuchen0cc]

LGTM