[CP-1698] Extends the set of valid HA restart priorities to include "0".
[CP-1698] Extends the set of valid HA restart priorities to include "0".

Signed-off-by: Jonathan Knowles <47466d50a94574c6fb872a0e5feec104dcb68f29@eu.citrix.com>

sharady/xcp-networkd,koushikcgit/xcp-rrdd,koushikcgit/xcp-rrdd,koushikcgit/xcp-networkd,johnelse/xcp-rrdd,djs55/squeezed,simonjbeaumont/xcp-rrdd,johnelse/xcp-rrdd,djs55/xcp-rrdd,simonjbeaumont/xcp-rrdd,koushikcgit/xcp-networkd,robhoes/squeezed,sharady/xcp-networkd,djs55/xcp-networkd,djs55/xcp-networkd,djs55/xcp-rrdd,koushikcgit/xcp-rrdd