Some more CheckPrereq/CheckArguments cleanup
Some more CheckPrereq/CheckArguments cleanup

For a few LUs, a few tests in, or even the whole CheckPrereq, can be
moved to CheckArguments, as they don't touch state and only do a 'type'
validation.

Signed-off-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>
Reviewed-by: Guido Trotter <f62ca4d5358bdaeef0e50e57f9f7e231de63727e@google.com>

andir/ganeti,ganeti-github-testing/ganeti-test-1,apyrgio/snf-ganeti,apyrgio/ganeti,ganeti-github-testing/ganeti-test-1,ganeti/ganeti,onponomarev/ganeti,leshchevds/ganeti,dimara/ganeti,onponomarev/ganeti,andir/ganeti,andir/ganeti,ganeti/ganeti,ganeti/ganeti,leshchevds/ganeti,apyrgio/ganeti,apyrgio/snf-ganeti,bitemyapp/ganeti,mbakke/ganeti,mbakke/ganeti,mbakke/ganeti,grnet/snf-ganeti,dimara/ganeti,yiannist/ganeti,yiannist/ganeti,bitemyapp/ganeti,yiannist/ganeti,leshchevds/ganeti,grnet/snf-ganeti