Initialize the variable to prevent a potential crash

In issue_mok_request(), old_req.Data must be intialized before
"goto error", or the process would segfault when freeing old_req.Data.
Only change terminal settings

tcgetattr() will fail if we send password through a pipeline instead
of a TTY.
Use getopt() to parse options
Adopt new password hash format

old format: MokNew + sha256sum(MokNew + password)
new format: salt + sha256sum(salt + password)
The new format makes a preset hash possible.
Close the key file
Get rid of misused while statement
Read the password hash from the file
Add a new command to generate the password hash
Amend help
New commands to revoke the import or delete request