In order to run on systems where not all requirements are present,
we should be tolerant of missing external dependencies, such as
psutil and pymysql. Print a warning (to stderr) and just leave out
those stats in that case.
Also make running the stats collector use ignore_errors:yes to avoid
failures in the future. I think the stats is not critical enough to
fail a job for bugs like this.
Related-Bug: #1970195
Change-Id: I132b0e1f5033c4f109a8b8cc776c0877574c4a49
1b601c7b1e