CP-18173 use common def of "is_true" for platform flag; improve naming
CP-18173 use common def of "is_true" for platform flag; improve naming

The xapi_vm_lifecycle module cannot use ocaml/xapi/xapi_xenops.ml where
Platform.is_true is defined as it would create a dependency cycle. The
code is currently dublicated here.

Signed-off-by: Christian Lindig <4f88b50bc9dba63c9a7d9e208d4b3ac6f1a52800@citrix.com>

rafalmiel/xen-api,Frezzle/xen-api,rafalmiel/xen-api,Frezzle/xen-api,srowe/xen-api,Frezzle/xen-api,rafalmiel/xen-api,rafalmiel/xen-api,euanh/xen-api,euanh/xen-api,thomassa/xen-api,Frezzle/xen-api,rafalmiel/xen-api,srowe/xen-api,euanh/xen-api,Frezzle/xen-api,thomassa/xen-api,rafalmiel/xen-api,thomassa/xen-api,euanh/xen-api,euanh/xen-api,thomassa/xen-api,srowe/xen-api,srowe/xen-api,euanh/xen-api,srowe/xen-api,thomassa/xen-api,thomassa/xen-api