Make the makefile not recreate ganeti every time
Make the makefile not recreate ganeti every time

Currently the makefile always recreates the ganeti symlink. Make it so
that it does only when it doesn't exist or it's not a symlink.

Reviewed-by: imsnah

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