ls-projects: Add --type to filter by project type

`gerrit ls-projects --type code` (the default) now skips permissions
only projects, restoring the output to what appears from Gerrit
2.1.7 and earlier.

`gerrit ls-projects --type permissions` will invert that output and
display only the special permissions-only projects.

`gerrit ls-projects --type all` will display everything.

Change-Id: If04bda437e45e51b5b071dac6edeb2a8ef730eb7
2 files changed