aconcli: Issues in command line syntax/flags

[binxing]

This issue tracks several (minor) problems in aconcli command line syntax/flags. These problems should be easy to fix.

• generate errs on existing FS layer symlinks
• generate should take output file name as a parameter and docker image/tag by a flag - as support to container tools other than docker may be added in future.
• export - --ignoresig doesn't seem to have been implemented. Also, do we have to check signature when exporting an image? Can we just export whatever available?
  • Report "unimplemented" when --ignoresig is specified.
  • Implement --ignoresig in future.
• ls and prune err on empty ACON image repo
• report missing flag/option to request a quote instead of a report
• report should generate nonce at random if not specified by the user
• stop and shutdown should have command line syntax/flags consistent with other commands - i.e., -c for specifying ACON TD/VM and -e for specifying container.
• sign errs on re-signing, also due to existing symlinks like in the generate command.

[binxing]

@xxu36, I found one more bug in sign that is very similar to generate - it errs on existing symlink. I've appended that the the tasklist above.

[binxing]

I'll look at ls and prune issues this week. @xxu36 please have a look at other task items.

[binxing]

ls and prune issues are fixed in #52

[binxing]

Let's implement --ignoresig now. For shutdown and stop command syntax, we may have to change if unix socket forwarding can work, so postpone to next release.