logcat: test: standardize rest() to let logs land when injecting

Add an internal rest() function to set the standard for how long we
should wait for a log message to land end to end into the logs.  Add
a retry on -EBUSY for all descriptive tests along with a rest() after
log injection so the tests can try to survive heavy Denial Of Service
(DOS) loads.  Some of the resting was done at a coarse 1 second, when
200ms will do just fine.

Fix a few pesky issues surrounding test reliability and correctness:
- stdint.h include missing.
- missing a logcat_executable, means logcatd.descriptive testing was
  testing logcat instead.
- count of interfering tests is 3 now: logcat, liblogcat and logcatd, if
  they all run in the same PID, we have to not fail.
- Added a missed opportunity to add uniqueness to logcat.descriptive sync
  test.

Test: gTest logcat-unit-tests
Bug: 31456426
Change-Id: Iaf2bee97878957f654613bb2e78e32379bb8d1b7