prevent memprof file overwrites for small intervals

Previously, the timestamp was accurate only down to seconds. For smaller intervals,
this would truncate the previous file(s). Now, for small intervals, the number of
microseconds is appended to the file name.

Added the possibility to disable timestamps in the memory profile file names and use
increments of 1 instead.

Updated the memory profiling integration tests.

docs/cgr-engine.rst

@@ -30,6 +30,8 @@ Able to read the configuration from either a local directory  of *.json* files w
         Interval between memory profile saves (default 15s)
   -memprof_maxfiles int
         Number of memory profiles to keep (most recent) (default 1)
+  -memprof_timestamp
+        Add timestamp to memory profile files
   -node_id string
         Node ID of the engine
   -pid string