Add parallel utilization

[AK2000]

Describe what the pull request does
Implementation of a utilization field for parallel profile types. This is used so that the parallel job then uses multiple cores of each host (#72). This is an optional field that by default is assumed to be 1. This does not change the behavior of the code when "core" is not defined for the host. When core is set, the parallel job is assumed to use the whole node (which seems to be intuitive).

Approach
The number of cores to use is calculated based off utilization in the same way as the usage trace. The computation and host vector are then repeated that number of times. The communication matrix is 0 extended, as if only the first core on the host is communicating across hosts.

Limitations
This could lead to higher overheads when core is set to a high number. Also, currently I support a single utilization number, which was enough for my purposes. It may be convenient to support a utilization per host vector, especially in the parallel profile type.
 
Alternatives
Originally, I intended to use the s4u::Exec::set_bound method. However, this is not supported for the L07 model.

Checklist

Branch name.

• Descriptive and short
• Use hyphens to separate words

Branch content.

• Only dedicated to the problem.
• Based on Batsim's official master branch.
• Straightforward. Just a sequence of commits. Does not contain merge commits.
• Test results are not worse than before. How to run Batsim tests?