man: mention changes in renew-crypto
man: mention changes in renew-crypto

This updates the gnt-cluster man page wrt to the changes
about server and client certificates and how they affect
the operation 'gnt-cluster renew-crypto'.

Signed-off-by: Helga Velroyen <2d0126b1ec6f9ec5cbec4a7012aa14faeaef10f5@google.com>
Reviewed-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>

andir/ganeti,mbakke/ganeti,andir/ganeti,bitemyapp/ganeti,grnet/snf-ganeti,yiannist/ganeti,leshchevds/ganeti,andir/ganeti,leshchevds/ganeti,ganeti/ganeti,bitemyapp/ganeti,ganeti/ganeti,leshchevds/ganeti,onponomarev/ganeti,mbakke/ganeti,mbakke/ganeti,grnet/snf-ganeti,yiannist/ganeti,yiannist/ganeti,ganeti/ganeti,onponomarev/ganeti