Description: Currently VIRL jobs schedule simulations round robin. At busy times this results in reaching the capcity limit of VIRL hosts, and tests fail.

Solution:  Adjust a VIRL simulation scheduling algorithm to verify VIRL available capacity via API, and schedule simulations based on available capacity. If no capacity, then wait similarly to how it's done for performance jobs using physical testbeds. Limit per tb4-virl host is now confirmed to 14 simulations per tb4-virl host due to currently available IPv4 mgmt addresses (14 * 5 = 70 addresses, 74 is current available number of /32s).