ustcweizhou 798b79fa5b kvm: disable cpu features if feature starts with '-' (#3335)
When I use SandyBridge as custom cpu in my testing, vm failed to start due to following error:
```
org.libvirt.LibvirtException: unsupported configuration: guest and host CPU are not compatible: Host CPU does not provide required features: avx, xsave, aes, tsc-deadline, x2apic, pclmuldq
```

With this patch, it works with the following setting in agent.properties:
```
  guest.cpu.mode=custom
  guest.cpu.model=SandyBridge
  guest.cpu.features=-avx -xsave -aes -tsc-deadline -x2apic -pclmuldq
```

vm cpu is defined as below:
```
  <cpu mode='custom' match='exact'>
    <model fallback='allow'>SandyBridge</model>
    <feature policy='disable' name='avx'/>
    <feature policy='disable' name='xsave'/>
    <feature policy='disable' name='aes'/>
    <feature policy='disable' name='tsc-deadline'/>
    <feature policy='disable' name='x2apic'/>
    <feature policy='disable' name='pclmuldq'/>
  </cpu>
```
2019-05-27 18:43:38 +05:30
..