lttng: VirtualMachineView: extract some methods to simplify the class

lttng: VirtualMachineView: extract some methods to simplify the class

This fixes some sonar warnings that methods were too complex. Some
repeated code was also extracted to a method so that both thread and CPU
entries can make use of it.

Change-Id: I18af32bfb2d16d63ee80e0bb1aba0664728ca633
Signed-off-by: Geneviève Bastien <gbastien+lttng@versatic.net>
Reviewed-on: https://git.eclipse.org/r/64617
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-by: Hudson CI