Added leap-util subcommand to check for a clean shutdown

[vladtr]

This PR adds command line option to leap-util to indicate if the last shutdown was clean or not. This would allow someone to better control logic about perhaps automatically starting from snapshot if the state database was crashed.

Examples of use:

Successful check with default state location:

./leap-util chain-state last-shutdown-state
Database state is clean

echo $?
0

Unsuccessful check with custom state path:

./leap-util chain-state last-shutdown-state --state-dir=/non-existent-dir
Unable to read database status: file not found: "/non-existent-dir/shared_memory.bin"

echo $?
255

After nodeos was killed with -9:

./leap-util chain-state last-shutdown-state
Database dirty flag is set, shutdown was not clean

echo $?
255

[spoonincode]

Should check that dbheader's header_id is expected value, as it's possible the format will change in the future

[vladtr]

thank you, done

[heifner]

Can you add to the PR description details about the new option and an example of the output.