api/server/router: use consts for HTTP methods
api/server/router: use consts for HTTP methods

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

cpuguy83/docker,estesp/docker,justincormack/docker,nalind/docker,moby/moby,dims/docker,SvenDowideit/docker,Mokolea/docker,thaJeztah/docker,pradipd/moby,jameszhan/docker,Ramzec/docker,moul/docker,jameszhan/docker,kojiromike/docker,kojiromike/docker,flavio/docker,nalind/docker,thaJeztah/docker,vdemeester/docker,ibuildthecloud/docker,jthelin/docker,yosifkit/docker,jvanz/docker,djs55/docker,nawawi/docker,AkihiroSuda/docker,bearstech/moby,estesp/docker,justincormack/docker,gnailuy/docker,konstruktoid/docker-upstream,ibuildthecloud/docker,docker/docker,trebonian/docker,bearstech/moby,AkihiroSuda/docker,paralin/docker,docker/docker,moul/docker,jimjag/docker,SvenDowideit/docker,moby/moby,SvenDowideit/docker,bearstech/moby,moby/moby,nawawi/docker,konstruktoid/docker-upstream,jimjag/docker,thaJeztah/docker,mahak/docker,mahak/docker,gnailuy/docker,nawawi/docker,konstruktoid/docker-1,AkihiroSuda/docker,konstruktoid/docker-1,docker/docker,moul/docker,jvanz/docker,estesp/docker,kojiromike/docker,Ramzec/docker,thaJeztah/docker,konstruktoid/docker-upstream,mahak/docker,paralin/docker,dims/docker,jthelin/docker,konstruktoid/docker-upstream,trebonian/docker,nawawi/docker,vdemeester/docker,nalind/docker,Ramzec/docker,flavio/docker,Ramzec/docker,trebonian/docker,ibuildthecloud/docker,paralin/docker,pradipd/moby,cpuguy83/docker,flavio/docker,dims/docker,moul/docker,cpuguy83/docker,vdemeester/docker,Mokolea/docker,Mokolea/docker,gnailuy/docker,jimjag/docker,yosifkit/docker,yosifkit/docker,trebonian/docker,jvanz/docker,flavio/docker,Mokolea/docker,djs55/docker,nalind/docker,moby/moby,yosifkit/docker,ibuildthecloud/docker,justincormack/docker,konstruktoid/docker-1,gnailuy/docker,jimjag/docker,mahak/docker,cpuguy83/docker,AkihiroSuda/docker,jameszhan/docker,pradipd/moby,ibuildthecloud/docker,djs55/docker,paralin/docker,bearstech/moby