add upgrade path to "cloud.dns.name" global config value.

fail creating GSLB rule if DNS name is not confiugred
CLOUDSTACK-2477: [GSLB] CloudStack currently allows admin to map LB rule
of one account to GSLB rule of a different account

ensuring account id of GSLB rule and LB rule are same
CLOUDSTACK-2285: [GSLB] addNetscalerLoadBalancer with GSLB functionality shouldn't be
exposed in basic zone

imposing restriction that NetScaler can only be added when EIP/ELB
service are available in basic zone.
fixing unit tests to comply with bug "CLOUDSTACK-2477: [GSLB]
CloudStack currently allows admin to map LB rule of one account to GSLB
rule of a different account"
CLOUDSTACK-2060
Global config to turn off dynamically scale vm functionality