[DOCS] Improve docs for "--pass" option in certutil (elastic/x-pack-elasticsearch#4352)
[DOCS] Improve docs for "--pass" option in certutil (elastic/x-pack-elasticsearch#4352)

The handling of the "--pass" option has complex rules due to the
different requirements of different output formats, and the way
joptsimple handles specs with optional arguments.

A standard unix shell will parse
    certutil --pass=""
as being identical to
    certutil --pass=
and joptsimple treats that as being "no argument", i.e. the same as
    certutil --pass

The only way to pass a blank password is
    certutil --pass ""
(though this is shell dependent)

Original commit: elastic/x-pack-elasticsearch@9af595749b5ff488e7112bdf67ced6d3756bfece

vroyer/elassandra,strapdata/elassandra,vroyer/elassandra,strapdata/elassandra,strapdata/elassandra,strapdata/elassandra,vroyer/elassandra,strapdata/elassandra