generate errors out if an action is specified that's the same as default

[grantseltzer]

For example:

17:33:40 grant in ~> ~ 
[*] oci-runtime-tool generate  --seccomp-default trace --seccomp-trace clone
default action already set as SCMP_ACT_TRACE

Instead, the default should be set to the specified action and a new rule just shouldn't be added specifically for the syscall... then the config should be printed as normal.

Other conflicting rules are just taken into account and generated gracefully. This doc explains the logic. That should probably be moved over to this repo as well.

[Mashimiao]

That' really a problem, we also have seccomp problem in default template. Maybe we can fix it after solve simple template problem #379