After spawning the "dnsmasq" process in the method
"Dnsmasq._spawn_or_reload_process", we need to check that the "dnsmasq"
process is running and could be detected by the ProcessManager instance
controlling it.
ProcessManager determines if a process is "active":
- If the network ID is in the cmdline used to execute the process.
- If the process is detected by psutil.Process(pid), returning the
cmdline needed in the first condition.
- If the PID file exists; this is written by the dnsmasq process
once is started and is needed in the second condition.
To make this feature available for any other process using
ProcessManager, the implementation is done in this class.
Change-Id: I51dc9d342c613afcbcfdc50a1d2811502748f170
Closes-Bug: #1849502
7c5ce50a0c