CP-6968: Add code to allow restarting gpumon from xapi

Signed-off-by: John Else <john.else@citrix.com>
CP-6968: Stop gpumon while VMs with vGPUs are starting

Signed-off-by: John Else <john.else@citrix.com>
Restart gpumon as part of xe-toolstack-restart

Signed-off-by: John Else <john.else@citrix.com>
Relax xencenter_min_verstring

Blocking XenCenter 2.0 means that Clearwater XenCenter will fail to
reconnect to a server after installing the vGPU hotfix.

Signed-off-by: John Else <john.else@citrix.com>
Revert "CP-5842: Update VGPU.resident_on for passthrough VGPUs"

This reverts commit de4ac0e62dad021b40c6cb525b2455e5868637ce.
VGPU.resident_on fix for passthrough

Set VGPU.resident_on for passthrough VGPUs with the same mutex as is
held when setting this field for virtual VGPUs.

This prevents both types of VGPU ending up on the same physical device
when bootstorming VMs with both types of VGPU.

Signed-off-by: John Else <john.else@citrix.com>