Document --ignore-errors and --error-codes
Document --ignore-errors and --error-codes

Update the man page of gnt-cluster to contain the documentation of the
--ignore-errors and --error-codes verify options. Also, include the list
of the error codes and their documentation.

Signed-off-by: Andrea Spadaccini <92d490849ac1b40cd8e8878e4d94603bebdb089f@google.com>
Reviewed-by: Michael Hanselmann <68b67885ff74281219b4a4be33cc20fd45078d7c@google.com>

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