Validate slice against available resources.

[kthare10]

• Added validation to add_node and add_component to check if the requested node/component is feasible to provision based on available resources on the requested site. This check can be performed as nodes/components are added. By default, it is disabled for backward compatibility and due performance hit caused by list_resources. Check can be considered to be enabled by default in 1.7 if needed once perf improvements for list_resources

• Added slice.validate() call to check the slice at the end. Users can invoke this explicitly to verify if their configuration is a valid config.

Code Snippet for Usage:
- Enable validation as nodes/components are added

# Create a slice
slice = fablib.new_slice(name="MySlice")

# Add a node
node1 = slice.add_node(name="Node1", site="RENC", host="uky-w1.fabric-testbed.net", check=True)
# Here node1 is invalid request would be errored and removed from the slice

node2 = slice.add_node(name="Node2", site="RENC", check=True)
node2.add_component(model='NIC_Basic', name='nic2')
node2.add_component(model='GPU_RTX6000', name='gpu1')
node2.add_component(model='GPU_TeslaT4', name='gpu3')
# Here node2 is invalid request as you can not have T4 and RTX600 both on a single worker

- Validate a slice

# Create a slice
slice = fablib.new_slice(name="MySlice")

# Add a node
node1 = slice.add_node(name="Node1", site="RENC", host="uky-w1.fabric-testbed.net")
# Here node1 is invalid request would be errored and removed from the slice

node2 = slice.add_node(name="Node2", site="RENC")
node2.add_component(model='NIC_Basic', name='nic2')
node2.add_component(model='GPU_RTX6000', name='gpu1')
node2.add_component(model='GPU_TeslaT4', name='gpu3')
# Here node2 is invalid request as you can not have T4 and RTX600 both on a single worker

# This call will report both the errors identified above
slice.validate()

[sajith]

Asking some questions, out of curiosity mainly. :-)