lxc: use job functions in lxcDomain* functions that perform modify actions.
lxc: use job functions in lxcDomain* functions that perform modify actions.

Use the recently added job functions and unlock the virDomainObj while
performing the respective modify operation.
This commit affects lxcDomain{DestroyFlags, Reboot, SetBlkioParameters,
SetMemoryParameters, SetMetadata, SetSchedulerParameterFlags, ShutdownFlags}

Signed-off-by: Katerina Koukiou <2601125deb717345fbc1a69eaf8ffe9a28fa5fe9@gmail.com>

eskultety/libvirt,nertpinx/libvirt,jardasgit/libvirt,taget/libvirt,fabianfreyer/libvirt,zippy2/libvirt,andreabolognani/libvirt,libvirt/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,VenkatDatta/libvirt,jfehlig/libvirt,eskultety/libvirt,olafhering/libvirt,crobinso/libvirt,jfehlig/libvirt,libvirt/libvirt,jfehlig/libvirt,crobinso/libvirt,jardasgit/libvirt,taget/libvirt,nertpinx/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,taget/libvirt,crobinso/libvirt,datto/libvirt,eskultety/libvirt,eskultety/libvirt,zippy2/libvirt,crobinso/libvirt,zippy2/libvirt,datto/libvirt,nertpinx/libvirt,datto/libvirt,VenkatDatta/libvirt,olafhering/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,eskultety/libvirt,libvirt/libvirt,datto/libvirt,jardasgit/libvirt,libvirt/libvirt,taget/libvirt,olafhering/libvirt,taget/libvirt,VenkatDatta/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,andreabolognani/libvirt,olafhering/libvirt,jardasgit/libvirt,nertpinx/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,zippy2/libvirt,datto/libvirt