[vdsm] Why do we need clean yum cache during bootstrap?

Hi Douglas,

Why do we need clean yum cache before installing packages during host 
installation?  It could cause a ssh timeout somtimes.  On my test VM, it 
needs several minutes do download yum metatada. Please see the test below:

[root@host1 tmp]# time yum update qemu-kvm
Loaded plugins: langpacks, presto, refresh-packagekit
fedora/metalink                                                                           
                             
| 8.6 kB     00:00
fedora                                                                                    
                             
| 4.2 kB     00:00
fedora/primary_db                                                                         
                             
|  14 MB     00:11
fedora/group_gz                                                                           
                             
| 434 kB     00:00
ovirt-nightly                                                                             
                             
| 1.3 kB     00:00
ovirt-nightly/primary                                                                     
                             
|  31 kB     00:00
ovirt-stable                                                                              
                             
| 1.3 kB     00:00
ovirt-stable/primary                                                                      
                             
|  15 kB     00:00
updates/metalink                                                                          
                             
| 4.6 kB     00:00
updates                                                                                   
                             
| 4.7 kB     00:00
updates/primary_db                                                                        
                             
| 5.9 MB     03:28
updates/group_gz                                                                          
                             
| 434 kB     00:21
ovirt-nightly                                                                             
                                            
183/183
ovirt-stable                                                                              
                                              
69/69
No Packages marked for Update

real    4m33.527s
user    0m5.741s
sys    0m0.772s

[root@host1 tmp]# time yum update qemu-kvm
Loaded plugins: langpacks, presto, refresh-packagekit
No Packages marked for Update

real    0m1.184s
user    0m1.048s
sys    0m0.115s


Thanks!
Mark