Add support for timer-specified runs.

Support compaction & backup for single-threaded runs.
Don't update the counters as often, should help with shared cache lines.
Merge branch 'develop' into format-timer
Make sure each thread has at least one operation to perform, but not
an arbitrary number.
Do operations if we have a time or an operation count.
Merge pull request #1372 from wiredtiger/format-timer

Format timer
remove tab characters from Python scripts.
When adjusting variable-length sizes, odd things can happen on the encoding boundaries.  Play it safe and iterate until we know the final size.

JIRA-16118
Fix the size adjustment issue by tweaking the encoding of one value so that packed sizes never decrease as values increase.
Merge pull request #1379 from wiredtiger/jira-16118

Fix for adjusting variable-length sizes