Document gnt-cluster upgrade in the man page
Document gnt-cluster upgrade in the man page

A new command, upgrade, was added to gnt-cluster. Document it.

Signed-off-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>
Reviewed-by: Jose Lopes <0fb9c4f8511df4ec2ae28af879e9d462f6218a2c@google.com>

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